YMMV, I'm finding that the HM1 sounds better at 110v in my system than 120v. The higher voltage might be a little more detailed and precise, but the bass suffers, background is not as dark, images not as rich and big, treble sounds a bit harder.
I think most are going to 120v as default, but in some (or many) systems, the lower voltage might sound significantly more musical and rich.
I also found that aftermarket fuses do improve the sound to a degree, but not as much as with other amps. I would guess this is because the power is still AC when it leaves the PSU/transformer box that houses the fuses. It's still worthwhile IMO, esp if you want more richness or warmth.