A huge difference between A1 and A2? No, not huge. But it was noticeable and made my digital sources more "analog" sounding. I'm glad I upgraded, but it was not night and day and A1 was very, very good sounding. As to Gen 5 USB VS Unison, that was an instantly noticeable improvement and is highly recommended, especially if you use a computer as a source.
Thanks, yeah I would be using a computer as a source and it would be replacing my Oppo 205, which I happen to like how it sounds. I just don't watch enough 4K Blu Rays to keep it, plus they are pulling quite a premium right now...