You can only have one power amp connected to your speakers at a time. Probably the best solution would be to use a speaker selector switch. I think that Radio Shack might even carry one.

Alternately, you might just use the single ended triode amp for your mains all the time - for movies and for music rather than the Outlaw 770. I would bet a week's wages that it would sound better than the Outlaw amp (sorry Peter!).

The only limitation would be power output, but SET amps clip so softly that you might not even notice it. Try it and see - you may be surprised!