I ended up going for the X-Fi titanium Fatal1ty. The shop didn't have Xonars in stock and reviews said it was about the same quality. Price didn't matter too much. Creative did piss me off with the Audigy2ZS/Vista drivers fiasco, but the X-fi drivers installed without a problem on Windows 7 so I forgave them.
Yeah my setup is 2.0. Just curious, why do you think a cheap external interface would be better? Less processing? (Also, I don't have any processing on the amp, it's just an amp with tone levels, no EQ etc)