Whatever you end up with - I'm REALLY interested in if you're going to throw the profiles up on the rig exchange of that particular amp
It seems to me that the Avalon needs a speaker connected still, so there seems to be no dummy load in that one.
I would probably look at a THD hotplate (may need t purchase used), or a Palmer DI. I've heard good things about those, but haven't tried them myself. Both of these are amp attenuators with line outs, I think. Also, beware of internet advice I'm really not sure what the best route is. Some people swear that speaker interaction is needed. Maybe they're correct, maybe not Couldn't hurt, I guess, if you can crank the amp without neighbours complaining.
The "virtual cabs" in the Kemper is actually the combination of the power stage of the amp and the cab. I think all other "cabs" are IRs, which are basically just an EQ curve, as I understand it - so they don't capture any interaction.