i just use the routing in my DAW & interface(behringer ADA8200) to switch between multiple speakers. Mono sum etc.
In reaper I have it setup this way now that if I press F1:
Unmute the LSR305's and mute the Avantone.
And with F2:
Unmute the Avantone, mute the LSR305's and also sum the stereo to mono on the master fader.
No need for spending money on another device to do this, also no extra possible audiopath that can breakdown

I used to have the M-Patch 2 before, and although it was passive it ****ed up my stereo imaging. So really glad with how it is now!