I sell both amps and listen to them nearly every day. I also own a VT100mkIII at home and lust after a REF110.
The REF110 is maximally open, liquid, and effortless in its presentation. There isn't even the slightest hint of grain. It's silky smooth and yet very uncolored and fast with excellent bass extension and control for a tube amp.
The HD220 is more powerful and tighter sounding, but not as open and 3D. It has some of the character of the REF110, but not all of it. It's an excellent amp for those who want solid state, less maintenence, less heat, less cost, and more power. Someone with power hungry speakers or low impedance might prefer the HD220.
Most others will likely find sonic benefits to the 110.
The REF110 is maximally open, liquid, and effortless in its presentation. There isn't even the slightest hint of grain. It's silky smooth and yet very uncolored and fast with excellent bass extension and control for a tube amp.
The HD220 is more powerful and tighter sounding, but not as open and 3D. It has some of the character of the REF110, but not all of it. It's an excellent amp for those who want solid state, less maintenence, less heat, less cost, and more power. Someone with power hungry speakers or low impedance might prefer the HD220.
Most others will likely find sonic benefits to the 110.