If you're using the preamp out signal of your amplifier, you will be getting zero coloration from the poweramp.
The only way you'll be getting coloration from a poweramp is if you're taking a line out from an attenuator, or something of the sort, or perhaps running your head into your Countryman as a load box, and then taking that signal.
I don't own a solid state power amp to be honest. If there is enough demand for something like that, I'm sure I could find one
AFAIK you can put a Countryman between a head and cabinet and take the line out from there, and it silences the signal.
AFAIK you can put a Countryman between a head and cabinet and take the line out from there, and it silences the signal. Giving it a quick shot couldn't hurt.