Connect. Please help

I have tube pre amp with 2 pre out. I have 2 set speakers. I have 1 stereo amp and set of mono block amp. 
Can i connect pre out 1 to mono block amp and pre out 2 to stereo amp, if i listen stereo amp I will keep the mono block OFF or listen mono block I will keep the stereo amp OFF? Thank for help
Pre Amp Unison Research Mystery 2
Mono Block  Vincent SP998
Stereo amp Parasound Halo A21