Pros: Lots of inputs/outputs, customization options, neutrality
Since the Gamma y2 is a DIY project I'm not going to comment on the build quality as its dependent on the builder.
The sound of the y2 varies on how it was built. Mine is using ASRC with standard parts, no special capacitors, power supplies, etc. Sound wise I don't notice any tonal changes when hooking it up to my Schiit Valhalla or speakers. Rather, the y2 improves more on the technical aspects of the sound. One thing I notice from switching back and forth vs on board sound is that everything sounds less mashed up and is spaced out much better. Soundstage seems to be increased and I get the feeling that sounds move outwards towards my head more. So, the y2 IMO is neutral and shows the more technical aspects of your music.
Another thing is that driving high impedance headphones out of the 3.5mm output worked quite well, my HD600 got to loud volumes and my y2 was not modified to drive headphones directly. However, the HD600 did sound somewhat limited being driven off only the DAC. The main drawback I found to driving right off the DAC is that I lose bass impact and control. Plus the soundstage crumbles. However, the differences were quite subtle. I can barley tell the difference between the y2 headphone output and my $350 Valhalla headphone out. I did a blind test with a friend switching the outputs for me. I was able to tell 38% of the time out of 40 short trials what the source was. (I was very embarrassed by the results).
I don't have much experience with DACs, the only other one I had was the Schiit Modi. However, from my memory, the y2 sounds on par if not better than the Modi. I didn't notice any major differences when I first heard y2 after leaving my Modi.
Features & Connectability
Anyway, the y2 also features other options like anti clipping and filters. Filters allow you to choose a different frequency roll off. Using a Sennhesier HD600 I can not detect any difference between filters A/B/C. Many other reviews say the differences are quite subtle and it will also depend on which DAC chip is used (WM8740,WM8741,WM8742). The y2 also has an anti clipping mode which attenuates the input by 2dB to avoid clipping, it seems to work well.
Another thing I enjoy about the y2 is it is flexible. You have optical, coaxial, 2x 3.5mm output, and an RCA output. As well as a plethora of digital input options. I had two amps hooked up to it at once (Fisher 400 and Valhalla) all via 1 RCA and 3.5mm output and it sounded excellent. I didn't notice any difference in sound quality when outputting to multiple sources.
The y2 is a solid DAC and I'm very pleased with mine, especially considering it's low price ($200) for parts alone and not including tools. (Can sometimes be found for even cheaper used). I can't find any negatives things to say about it!
Thanks for reading!