Guys,
I own a K12 and an HPR122i and I also run the Axe thru a VHT 4x12D cab powered by whatever is handy for power.
Now that I know the Axe and these bits of gear well enough, I can make it sound good thru any of them, though some are more flexible and easier to tune for me.
Speakers are an absolutely huge part of your sound, as are all the other details, but with a little effort I've yet to ever think "Ick, the Axe sounds like poop thru that." especially in the context of a rock band where a lot of detail is, let's be honest, lost to cymbal crashes after 5 minutes or you were wearing earplugs and never heard the top end difference in the first place.
The K and the HPR definitely require slightly different EQing and have different sweet spots in my use but both work.
I use the K at home b/c its smaller and the HPR at practice where the size is a win and I get a little more woody resonance which, "accurate" or not, I enjoy.
I've never run them together in stereo and look forward to trying it on vacation in August when I have hours to wank. The differences might make a fun stereo image.
-P