I have the US16x08. It works well for me. I bought it a year and half ago, but I've really just started using it regularly in the past several months. Most of my recording had been live stuff using my Zoom R24, mixed down in Reaper, or before that, on my Yamaha AW1600 and AW16G. Using the 16x08 with Reaper is amazingly easy. I was fooling around the other night with a friend, letting him try doing a vocal track on a practice recording that we did about 10years ago on the AW16G but never finished. The first 8 tracks were dumped from the Yamaha to Reaper, and I've added electric and acoustic guitars and vocals using my Tascam.
Honestly, I wish working with tape was that easy. But if you are doing a performance recording, it doesn't matter if its going to tape, hard drive recorder, or computer. Hit record and start playing. Hit stop at the end, and you've got it.
One thing that came to mind was that using the US4x4, you should be able to do both a tape recording AND a direct digital recording at the same time. That way you could really compare the two as they would be getting the exact same feed.
In any case, I'm sure you'll have fun. I enjoy playing with all this stuff! My only regret is that it wasn't this easy and this cheap 40 years ago!