not too many reviews though. would be interesting to see how the AK4452 sounds/performs
The Sabaj D4 isn't bad. Especially once I started using it in my headphone setup with my Massdrop Cavalli Tube Hybrid headphone amp. While I can't objectively prove they made any difference, changing the filters from the "acoustics" settings (there's a separate "Sound" filter, that I don't know what it does, as there's no manual online and my box is in storage) helped when listening with headphones as it sounded subjectively kinda fuzzy before. I can't objectively prove a difference beyond "changing a setting made me feel better."
Otherwise, issues I've had:
- Headphone output is noisy with sensitive IEMs and has unknown output impedance, but it didn't make my ATH-IM02 noticeably brighter as high output impedances tend to do. Also, it's a 3.5mm output, you might prefer 6.3mm.
- The screen is quite small, so it's tough to see it from a distance
- No buttons for directly switching to inputs – the input changing button goes USB->Bluetooth->Coaxial->Optical – so setting up with something like a Harmony remote would be tough.
- Volume settings are shared between headphone and line output. What happens is that if your volume is above 20 (out of 40) then when you switch from line output to headphone (I much prefer the switching with the remote button, as opposed to it happening automatically) the volume gets set to 20. This is good so that you don't blow up your ears or sensitive headphones (this thing can drive my HD580s quite well, though based on my experience and listed power output, you might not want to use this with low-efficiency and low-impedance planars) but might make it a bit annoying if you don't need the variable output.
- The buttons on the device are capacitive, and not the most responsive. Some things, like Bluetooth pairing, might be impossible from the device itself, and would work only through the remote.
So yeah, there are a lot of little quality of life issues or features that you might prefer operate differently. However, when I was using it in a less-critical situation as a preamp for my JBL LSR305s in my TV setup that occasionally played music, it sounded great. And once I messed with those filters, I got to be a lot happier with the sound of it. And as a headphone amp, as long as you're not using sensitive IEMs, you won't have a problem with it.
Honestly, I think that I'd only really recommend it if you need a DAC with remote control, as it's the cheapest viable option I've found, and it does a good job with that! But without a remote, you can do quite well for yourself in the price point, can get the D50 for $50 more, or even a good DAC/amp combo if you need a separate headphone amp.