As an owner of a Reference 110, I would say that if you want the maximum tube bloom, musicality, and midrange presence, the REF110 will do a wonderful job, as long as your room is not too large and you do not need to play at extremely loud levels, for long periods. But to realize the full bass dynamics and speed of the Vandersteen 3a sigs, the HD220 can do do a better job. And you can play as loud as you want, for as long as you want, with no output tubes to replace. One other thing: if you often experience some line-voltage variation such as a dip of 8-10 volts or more, then I would also lean toward the HD220. Tube amps need consistent line voltage for both best performance and best service life from the output tubes.
I think, either amp will give you wonderful results, with slightly different sonic shadings.
Hope this helps you make your decision.