Don't do it. It's sort of blasphemous to pair a Marshall power amp with a Boogie preamp. OK... but some guys do it and like it. So maybe do it.
1. If you love Boogie tone, don't do it. The EL-34 based Marshall power amp sounds very different than a 6L6 Boogie power amp, and the Simul-Class 2:Ninety in particular has a VERY unique signature sound that gives the Marks series its tone.
2. Pair that Marshall power amp with the Marshall JMP-1 MIDI Tube Preamp for classic Marshall tone. I played this rig before falling in love with Boogie tone.
3. Marshall power amps are NOISY!!! With high gain sounds in your Triaxis, I'd bet you'll need a noise gate (a stereo one, of course). The Boogie power amps are extremely quiet, especially the 2:Ninety. I had one of my Marshall power amps modded just to reduce the noise.
Scott