Sim Audio i-5 or Bel Canto s300id integrated

Go with the Sim. more powerful sounding, ability to drive a wider range and better bass.
Also consider Plinius.
Type of speakers you are driving would be helpful.

The Sim i-5 is a better sounding piece IMO. I had owned the Bel Canto unit but didn't like the discontinuity between the bass and the midrange/highs. By this I mean that the bass was very present/solid but sounded different/out of place with the rest of the range. This is due to how the implemented their digital amp technology (which is still a nascent audio technology). I currently own a Sim integrated and am very happy with the sound. A natural sounding unit with very good soundstage placement.