Can I Use One Channel Of A Stereo Power Amp?

Although not cheap, the MBL 9007 can be used both ways. Generally they are sold as 440 wpc mono amps but they can also be used as a stereo amp. When in stereo mode the power is greatly reduced to somewhere around 130 wpc.

Play it safe and call the manufacturer of the amp if they are still in business.

I always use a dummy load on any unused outputs. An 8ohm, 10 watt resistor is all you need to protect your amp from accidents. This, by the way, is more necessary with tube amps than with solid state. I do not know the theoretical reasons for this.