I've only had an hour or so with the MKV at shop volume levels but I'd say not entirely Apples and Oranges. The Triamp has EL34's in the output stage and is designed to emulate Fender, Vox, Marshall Plexi, JCM800, Hot rodded Marshall and I'd say Soldano/Boogie on the last channel of the six. IMO it does all of these pretty well with a certain amount of H&K's own flavour thrown in. The Triamp can be a very 'smooth' sounding amp much like the MK series of Boogies. I remember many complimentary comments about the tone (and looks) of the H&K when I was using it live and have missed it since having to let it go. I have more experience with the MKIV than MK V and to be fair I used to get compliments on the tone of the MKIV as well. There's no doubt (in my mind) that the Triamp is a more versatile amp than the MKIV, but the MKV may well be a different story, although only 3 of the MkV's 9 modes are foot switchable compared to the Triamps 6 modes which are all switchable. I always found the Triamp easy to set up though and you'd have to have cloth ears and a ham fist to make it sound bad. It's a very cool sounding and versatile amp.
If I had to choose between a half stack MK V and Half stack Triamp the decision would be very difficult. Both set-ups would cost about the same here in the UK. Not having tried the MKV at gigging volumes where it obviously shines the comparison is a difficult one. I hope to re-demo the MKV soon but the Triamp is still up there with it on my list.
Another cool demo of the Triamp:-
http://www.youtube.com/watch?v=sbXIrtqCGrQ
