Thank you on the 3 points. I think for times when I need the bluetooth convenience, iFi will do just fine. That said, regarding your second point on coax...I don't really know how the processing works
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I definitely would like for the miniDSP to process, and I assumed coax was best since I will most likely purchase the SHD Studio, and the optical will be taken up by the TV input. Maybe there is a bluetooth receiver with XLR output? Or is it better to connect bluetooth receiver by the RCA? I don't mind buying SHD instead of the digital-only Studio version if that is the only way for miniDSP to control the processing. The upcharge is not significant.
As for DAP, I'll probably stick with LG since it fully unfolds MQA. Seems easy and USB C to USB 2.0B works. I'm not very keen on ethernet streaming.
I think I understand now where you are coming at this from. I was confused about why you wanted coax output from a BT receiver. Also, on re-reading my previous post, I realize that paras two and three are ambiguous and as a result likely confused you; my fault and I apologize for not being explicit. When I wrote "Not sure what the iFi Zen Blue is putting out over coax", I was puzzling about the quality of the signal, not the format. Definitely the iFi is outputting S/PDIF over 3.5mm coax which is basically PCM limited to 24-bit 96kHz, IIRC. It should be perfectly compatible with the coax input on the SHD Studio and SHD. Also, when I mentioned the HiBy R3 Pro, I meant it as an alternative to the iFi Zen Blue, and not to the LG. The R3 Pro has two-way BT including LDAC and UAT, and can receive BT/WiFi and output S/PDIF over coax to the miniDSP (though this needs to be verified).
As I understand it now, you have settled on an LG premium phone for its low cost to you, its all-in-one convenience, its fairly good DACs and its full MQA unfolding capability. I should have kept your thread title in mind LOL. Also, you have settled on a miniDSP SHD Studio for its DSP/Dirac features, but might consider a miniDSP SHD instead for its added analog input capabilities. I understand that when you want the highest SQ, you can connect the LG directly to the SHD Studio using a USB-C to USB 2.0B cable, but you also want to use Bluetooth with best possible SQ at other times, for convenience. I understand now that you wanted to have coax out on the BT receiver for compatibility with the SHD Studio, and not necessarily for higher quality of sound versus analog out, though you would like to maximize the SQ as well. I did not previously know anything about miniDSP, but I took a look at the back panel I/O of the two models on the miniDSP site, and now I understand.
I am not sure what the equivalent uncompressed PCM datarate is for 320 kbps MP3 with today's encoders, but it is higher than 320 kbps and less than 16bit/44.1kHz of CDs, closer to the latter. The audible significance, and even the very audibility of (EDIT: sound quality differences due to) anything higher than the PCM equivalent of 320 kbps MP3 is a contentious topic, and I will let you fret about it. I will speak only of datarates and SINADs.
As member PaulD pointed out, the sonic and other benefits of MQA are questionable, but I quite understand that you already have access to MQA and want to hedge your bets. Incidentally, HiBy tout their new R8 DAP as able to do 16X MQA unfold, which I have never heard of before. One version of the R8 can also stream data/music over its own 4G connection. Of course, the R8 will cost more than the miniDSP SHD and more than the LG phone, LOL.
If you listen to MQA-encoded music just on your LG V40, with earphones/headphones or a Line Out to an amp, the LG will according to you do a full MQA unfold to a puzzle of a MQA bitrate and convert to analog using the LG V40's ES9218P DACs, giving you an output electrical signal and a SINAD of up to 112 dB at the phone's audio jack. Also on your LG phone, you can listen to non-MQA FLAC/DSD up to 32-bit 384 kHz PCM and DSD512 bitrates (which of course blow away the MQA bitrate) by virtue of the same ES9218P DACs, also giving you a SINAD of up to 112 dB in the analog electrical signal.
The right streaming/playback software on your LG V40 or your computer can perform the MQA decoding of MQA-FLAC to PCM with embedded folded MQA data, which you can output to a Topping D90 MQA via USB. By doing this also, you can get a hardware full MQA unfold (upsample, filter and render) with its mystery bitrate, and get an electrical analog out from the D90 to your amp with a SINAD of 120.5 at the D90's audio jacks. With non-MQA PCM files, the D90 and D90 MQA can process up to 32bit/768kHz input with an analog output signal SINAD of 120.5, well beyond a guaranteed audible transparency threshold of 116 dB.
The miniDSP that you need in the path to do DSP/Dirac Live changes the picture. Both miniDSPs resample digital streams internally to 32bit/96kHz, although they can accept up to 192kHz digital input signals. The miniDSP SHD additionally uses an AK5574 ADC chip, with a 32bit/768kHz sampling rate and SINAD of 112 dB, to convert analog input signals to digital PCM streams; so the ADC quality is more than adequate to match the internal 32/96 digital bitrate. Of course, the DSP and Dirac alter the SINAD of the signal, but this is desirable distortion that you need to correct the acoustic room resonance distortions. Both miniDSPs are non MQA-capable and so cannot do unfolding of MQA. Neither miniDSP can do a bit-perfect pass-through (if they could, why are they in the path at all?) of a digital stream.
As member Vincent Kars pointed out in post #7, passing a (decoded) MQA-PCM stream through the miniDSP would destroy the MQA watermark. Thus, no hardware unfolding of the MQA-PCM is possible by a MQA-capable DAC placed downstream of either miniDSP and fed by the latter's digital output. In this scenario of a digital stream decoded to MQA-PCM, but not hardware-unfolded, and passed through a miniDSP, the digital output stream of the miniDSP would have a PCM bitrate that MQA claims is slightly better than CD quality but most expert commentators say is slightly worse than CD quality 16/44.1.
Therefore, with a miniDSP in the path, the only remaining option to get the benefit of hardware MQA unfolding is to do it with a MQA-capable DAC upstream of the miniDSP. This could be done entirely in the LG V40 or with the LG V40 + Topping D90 combination described in previous paras, resulting in an analog line output signal that requires the more expensive full miniDSP SHD version with analog inputs rather than just the digital I/O-only SHD Studio version (unless a ADC is applied to the analog signal to get a digital signal, which is what happens with Bluetooth). The output signal from the SHD would then be equivalent to a max bitrate of 32/96 and a max SINAD of 112 dB.
Inserting Bluetooth into the path once again changes the picture, as pointed out by members PaulD, pirxel, Jimbob54 and Vincent Kars. Bluetooth resampling for the selected BT encoding scheme will destroy the MQA watermark, and so any hardware MQA unfolding must be done upstream of the Bluetooth segment of the path. The Bluetooth effective datarate will also act to limit the max quality of the signal, depending on the codec used. WiFi streaming may be better in this regard, and may even be able to preserve the MQA-PCM bitstream (unlikely though).
If you are able to do LDAC BT with its 990kbps bitrate, you may get close to 24/96 PCM bitrate quality BT streaming. Otherwise you are stuck with aptX HD and roughly CD quality PCM bitrate streaming. It indeed seems like the iFi Zen Blue you found and linked is a good option as a BT receiver, save for its current scarcity/unavailability. In this case, since the iFi has a S/PDIF coaxial output, you do not need the full SHD, you can stick with the SHD Studio instead and save yourself some money. Your chain would be LG V40 MQA decode and full unfold, BT to iFi ZB, coax to SHD Studio, opt/coax output to your amp or active speakers. Your overall electrical signal will have the equivalent of a 16/48 (aptX HD) or 24/96 (LDAC) PCM bitrate, and whatever SINAD the Bluetooth resampling cuts the LG's 112 dB down to. If you use the analog output of the iFi ZB instead of the optical/coax, the SINAD drops to about a mediocre 96 dB for a hard-to-fathom reason. Hopefully, the optical and coax digital outputs do not suffer any such degradation. EDIT: In case the S/PDIF optical and coax outputs of the iFi ZB are not up to par, the HiBy R3 Pro might be a high-quality alternative. Alternative devices are BT receivers such as member Vincent Kars linked to: FiiO BTR5, Shanling UP4, Qudelix 5K. But these would give you analog outputs, and require you to get the full SHD instead of the SHD Studio.
