hifi engine

Use of center channel and addition of sub-woofer through McIntosh C26 preamp

The heart of my home audio system is a pre-1976 McIntosh C26 preamp which feeds through an even earlier McIntosh 150 transister-type power amp (65 watts RMS each channel). They drive 2 - three-way sealed Infinity Quantum 5 loudspeakers through the preamp's main speaker switch, oriented as "front" speakers and 2- five-way custom-built sealed speakers through the remote speaker switch, oriented as "rear" speakers. The bass response of the rear speakers is pretty clean and awesome, but I want a little more "oomph."
I have never used the preamp's center channel, which combines L & R, but I am interested in upgrading the system by adding both a center speaker in the front and a subwoofer in the rear.
Can I effectively hook both a front center and a rear sub woofer to the center channel output of the preamp? If so, do I need a powered subwoofer?
Also, based on the assumption that I can do the above, can I get a recommendation for what brand names or performance specs for both?

Use of center channel and addition of sub-woofer through McIntos

Please forgive me. To clarify my latest posting, my power amp is a McIntosh 250, not 150. I've only owned it 34 years. To avoid 'clipping', the gain controls cannot be beyond half way. Is this condition an anomaly?