The new amp may not have quite enough power power to drive the M5's. If you don't have a big room and listen at high volumes, you'll probably be OK. If you do a lot of off axis listening, you may want to keep the M5's. If not, the Vandersteen Model 1's would be a good choice. Easier to drive, and they do things the Mirage can't do. But they have a sweet spot, and if you're not in it the difference will be noticeable.
Speaker experience/recommendation for CJ Classic60SE
I have an opportunity to replace an old CJ MF200 w/ the above for a very favorable price. Not my primary system - CJ PV11 and Mirage M5si in a teaching/music writing studio but wondering what a more modern speaker might be better suited to the Classic 60SE. Of course it may make the Mirage even better, it's still an interesting and engaging speaker