Don’t see the point in having a pair of stereo monitors both playing the same mono channel.
I’d do the opposite, running the FRFR as a mono source, and then stereo to the monitors.
Basically a wet/dry/wet rig. Given the FRFR will likely dominate the monitors (I have s6’s myself) having the frfr be the mono dry source would also make more sense, with the monitors then giving a nice stereo ambience.
I do basically this same thing, one CLR for dry, but instead of stereo monitors, I use a Centerpoint Space Station for a pusedo stereo wet sound but from just one source. Man it sounds killer with things like a rotary speaker