I'm gonna sell my JVM410H too, but only because I picked up a JVM410HJS, and it's in a whole different league. I think the FX8 is better suited - by design - to work 4CM with an amp. You have true bypass and unity gain. So, I could see where using the AX8 in 4CM might compromise the tone a bit. Fractal has been pretty open about the differences in design philosophies between those two units.
I wonder if the OP might get better results just using the JVM as a power amp in a live situation instead of using it 4CM. You'd still have the resonance and presence controls to adjust to the room, but you'd have access to all the models on the AX8 (including JVM models).