I have a Vintech Dual 72 and have used the UA 610 preamp. Different beasts. I preferred to buy the Vintech, since I'm more into the "N" word sound than tubes. UA is softer, maybe rounder. I find the Vintech punchier, and it cuts in the mix a bit better. Also, it has something that makes things appear to be more in-your-face. Love it. But hey, if you want big punch, go for API, if you want balls, "N" clones (if you can't afford the real thing, but the Vintech is so close it's scary. at least for the tests I made).
Never used the 2108, so I don't know how different it is from the 610.
andr