Here is what I have experienced:
1) SRC is the best-sounding software upsampler for Foobar2000, at 24/96
2) Hardware upsamplers all sound about the same, not so great IMO, with one exception: for 24/192 upsampling, the SM5847AF chip is wonderful. Implementation is everything though. You can still screw it up with a bad design.
Steve N.
Empirical Audio
1) SRC is the best-sounding software upsampler for Foobar2000, at 24/96
2) Hardware upsamplers all sound about the same, not so great IMO, with one exception: for 24/192 upsampling, the SM5847AF chip is wonderful. Implementation is everything though. You can still screw it up with a bad design.
Steve N.
Empirical Audio