If you haven't already chosen amps, consider using a pair of tubed stereo amps in mono. With a tubed amp, one merely runs the 2 channels in parallel and ends up with the combined power into half the indicated output impedance. For instance, an inexpensive c-j MV75, rated at 75 WPC into 4, 8, or 16 ohms, becomes a monoamp capable of 150 watts into 2 or 4 or 8 ohms. There are lots of medium-power, stereo, tubed amps (such as the c-j Premier Eleven) that are excellent candidates.
I'm currently running a new-to-me c-j Premier Eleven-A (70WPC) in stereo driving my quite-efficient (94dBA) L/R speakers and just bought an inexpensive c-j MV75A that I'll use as a 150-watt monoamp to drive my low-efficiency (85dBA) Aerial CC3B centerchannel speaker.
Good luck.
I'm currently running a new-to-me c-j Premier Eleven-A (70WPC) in stereo driving my quite-efficient (94dBA) L/R speakers and just bought an inexpensive c-j MV75A that I'll use as a 150-watt monoamp to drive my low-efficiency (85dBA) Aerial CC3B centerchannel speaker.
Good luck.