Is It Safe To Connect Speakers To Two Amps??

i've got a combined HT and 2-Channel rig whereby my mains and subs function in both. i'm currently using the traditional connection scheme whereby the HT processor sends signals to the mains via the pre outs to my preamp (in bypass mode) then on to my main power amps, then on to the speakers.

if i wanted to bypass my preamp and main power amps althogther (it's a shame to burn tube hours on movies), is it safe to simply connect my main speakers to the HT processor via speaker level connections if they are also connected to my main power amps concurrently? only one amp - HT processor OR main amps - would be running at a time.

any inputs would be greatly appreciated.