Hey Rob,
I agree that every amp generates a different sound, and this is specially true for non-linear amps such as those for electric guitar.
OTOH, many excellent session men (see the Dave Cleveland video on YT) and famous studio engineers (M.Wagener) have been saying they can't hear any difference between the Profiler (linearly amplified and with a properly-taken profile) and the original mic'ed rig, neither in timbre not in feel.
Now, if you move from there and add further colouration to the sound, for example through a guitar tube (non-linear by definition), you're actually moving away from the original sound, not getting closer.
Have you ever profiled an amp of yours, and heard it back through a very neutral system?
Anyway, if you want to use a tube power amp, the only currently available solution AFAIK is using an external tube power amp, be it a rack or the return of a combo.
HTH