Hello to everyone.
I'm a recent owner of the Z6 and although i have been doing some research prior to buying it, i noticed that there aren't many reviews of these 2 devices. Yet.
After reading the ASR thread about the Z8 and noticing there are quite a few people asking about the Z6 as well, i'm gonna write a few words about my own (obviously subjective) experience with the device, in hope that it will help at least a few of you guys here.
I was lacking a dedicated DAC in my audio chain (had a dedicated ASUS sound board) so i went to a specialized audio shop, 300 km away from my town, to have a chat with the guys there (they are the best in business, here in my country) and ended up with the Z6. I already had a Woo WA6 2nd gen with NOS tubes and was hoping that i could, maybe, "clean" the audio signal a bit. Listening is done on 2 pairs of headphones, an Arya SE and LCD-2 Bamboo (fazor). The chain is PC (Foobar2k) -> Z6 -> Wa6 -> Headphones. Mostly FLAC, locally stored, files.
First impressions were... tiresome, to say the least. After more than 1000km driven (had to take a few detours), i couldn't help myself and jumped right into it. The Aryas were unbearable to listen to, at higher levels. I felt like my ears were bleeding and yes, i am highly sensitive to sibilance, high freqs, the works. I look for a warm sound signature but i also enjoy a more neutral(ish) one, too. Before this, straight from the pc's sound board, the sound seemed more tame, more warm. The issue is that besides bringing a new device into the chain, i've also swapped the power/driver tubes with a different NOS pair so i've said to myself that it's a mix of new tubes, excessive exhaustion on my behalf and the Aryas being a bit too bright, at times.
So after a long night's sleep, i made the biggest coffee mug i could find and sat down, powered everything on and started listening to music. I listen to all genres (from classical to 60s, 70s, 90s, trance, ambient, psy, progressive, rock, etc.) so i started with something more laid back (Nibana - Aeon) and lo and behold, when my body isn't at the brink of collapsing, my brain (through my ears) is also better functioning. So the music is exactly as i have hoped it to be. Neutral-warm sided with plenty of volume left on the WA6.
Now for the Z6 - i keep it at 0 db gain and use the amp for volume tuning. It's connected via USB-B to my PC and through 2xRCA cables to the WA6. I couldn't hear any sort of background noise (or at least anything *new* to what i could already hear). It has 3 filters and although i couldn't hear any difference between them, i've left it on the slow roll-off one (the middle filter). It does, indeed, have 3 VU meters and everything can be controlled from within the app (iOS, in my case). There is a bit of a delay when changing something from within the app and sometimes, some options are stuck in some sort of a loading state. Restarting the app fixes it.
I also tried listening straight from it's 6.3 headphone-out port, on the Arya and it managed to drive them to a decently loud volume (not brain cooking loud but loud enough that if you aren't partially deaf, you'd be able to enjoy the music). It sounds more neutral, at least to my ears, when compared to the WA6 but not by a huge margin. The volume know works flawlessly and it's also the main control option, if you choose to use it. You can press and, obviously, roll left or right to navigate through the menu.
Streaming to it via Bluetooth works without any issues (so far). I was able to stream via aptX HD (i don't have a better bluetooth device, with LDAC or Adaptive, on hand),
One issue i have been encountering are some small interruptions in music playback. It happened 4 or 5 times, so far and the first time it did, was when i used a magnetic tape measuring device, so i could measure the dimensions for the furniture needed to stack the devices (the woo has too big of a depth to be able to stack it onto the Z6 and viceversa is a no go, due to the tubes / transformer sticking out). Then, today for example, it happened again while simply listening to it. I do have a small magnetic device next to both of the units (a QI charging pad) but that was there since forever and it never happened before.
Build quality seems top notch, the package comes with a normal power cable and a USB-B to USB-A cable. I haven't tried the USB-C port but i will, since i have a few cables laying around.
I was also able to test the Z8, at the same store. I wasn't particularly interested in it, since i already have a dedicated desktop AMP and due to the audition being done on a different chain than the one i have at home, my impressions are heavily skewed and subjective but what i noticed, first hand, was a higher volume coming out from the Z8 (they had a pair of SE Aryas for testing, among other headphones) but if my memory serves me right, nothing that can compare to what i can output back home. Still, high enough that i felt discomfort during, say, Enigma's Between Mind and Heart song so i had to lower it by a few dbs. The Z8 also has 4, i think, more filters than the Z6 and 2 or 3 more VU meters (since i can't tell the difference between any of the filters and the 3 VU meters that the Z6 has are more than enough for me, i don't find these as good selling points for the money difference). Connectivity wise, they are the same. The display is the same. The amp stage is better on the Z8, at least subjectively and the DAC section is the last element that differs. Z8 has a single ES9038Pro, compared to the dual ES9068 of the Z6. Sonic wise, they were the same (again, subjectively).
So in my opinion, for someone who already has a dedicated AMP or for someone who isn't using very hard to drive headphones, the Z6 is the price/performance champ, between the two. On the other hand, if you are buying the Z8 for it's amplifying capabilities, you're wasting money since it won't be able to properly drive, say, a pair of HD800s or some hungry planars. Come to think of it, i can't exactly figure it out for whom, exactly, was the Z8 designed but this might be my buyer's bias.
Hope my useless rambling helped at least a few of you and if you need any additional information about the Z6, feel free to chime in and i'll do my best to help!