I used to have a Sim I-3 (regular version) in my set-up, then after trying out several other amps, I settled on a NAD M3, so my impressions aren't side-by-side, and should probably be taken with a grain of salt. That being said, I found that the NAD was simply much better than the I3 in all respects--resolution, soundstage, pacing, etc. Of course, given the respective price points for these amps, that's probably to be expected, and I do think that the I5 might be more comparable to the M3. The M3 does output well over double the wattage of the I5, though...