Thanks afu. Perhaps I could have been more clear in my original post as to what I am trying to accomplish. I have no intention of muting the RK2's power amp (it is a combo btw). Instead I am building a Mix/Dry/Mix setup. Same idea as typical w/d/w but the stereo mix cabs are the dominant factor, with the combo running dry to maintain clarity and punch when using wide stereo FX like dual delays etc.
I built a rig like this years ago with a Marshall 6100 as the dry and two JCM800 2203's as stereo power and it sounded fantastic. The Slave Out on the Mesa is a different animal than the Marshall's Line Out however. What I am getting at is, because the Slave signal is post-power amp, would using a (big) tube power amp for the stereo side be an issue? Too "tubey" if that's even a word?
So, I see my options as: use the Slave Out into a 2:90, 2:100, 9200, 2/90/2 or similar, or a healthy SS power amp if the RK2's influence is an issue. (Easiest if it works.)
Or take a split from one of the FX loop sends using a pedal with a "dry thru" or dual outputs to get the RK's preamp to my stereo FX without muting the RK power amp. ( maybe a better solution as the stereo amp can have it's own thing going, regardless of my choice of output tube combination in the RK)
OR modify the Slave Out. (Probably the ideal solution, provided it doesn't require re-engineering the whole amp) Seems like it should be a simple mod. I'm thinking disconnect the slave level pot, and jumper it to the FX send pot so they are in parallel. I know which end of a soldering iron to pick up, but this is a complex and expensive amp and I really don't want to experiment on it. Pot values if they need to be changed, impedance issues, other parts needed etc. Anyone with knowledge of this please chime in.
I realize the second and third options would limit my power amp choice to the 2:90 or 2:100 or similar, with a switchable "Modern" option so it tracks along with the RK volume-wise. Not really a bad thing, those are both killer amps.