I suggest you also consider the VS-115. I am very happy with mine, paired with a REF 3 preamp. I also auditioned the 110 and the 220. I vastly prefer the 115 and 110 over the 220 and the 110 and 115 are very close to each other in sound though not in price.
Audio Research REF-110 vs. HD-220
I have a REF-3 and an ARC CD-7 and I'm planning on upgrading my ARC Classic 60 for either the REF-110 or the HD-220. I have efficient, full range speakers (92db Legacy Sig IIIs). My question is: have any posters here had the opportunity to have both amps in their systems long enough to be able to say what the differences are? I listen mostly to jazz, female vocals, light classical, classical guitars and some large orchestral music. Tonal accuracy is very important to me, as is the emotional impact of the music. I'm much more the music lover than the audiophile. Thanks ...