Jeff M.
The DXR-12 is a great (and popular) FRFR wedge ...but ask around and see if you can test out an Atomic CLR powered wedge.
Outstanding sound - super wide sweetspot!
Don't forget to swap out different cabs to get different flavors.
I profiled my '82 JCM-800, but replacing the cabs really opens it up "absorbs" the cab/speaker character.
Haven't turned on the Marshall since I profiled it
I drove the locals crazy looking at powered wedges.

Even though the QSC K12 is a great stage monitor, it was one of the worst sounding for this application.
Gaping hole in the mids... due to the cross-over.
Couldn't find anyone local with an Atomic CLR (heard nothing but great comments).
I'm very pleased with the DXR-12.
My wife even commented on how good the Kemper/DXR-12 combination sounds.
She walked in thinking I was playing the (real) 5150>2x12.
I'm just getting started with the Kemper... and already I find myself forgetting that I'm not actually playing thru a (real) tube amp.