I was wondering if I used Y connectors at the power amp and ran ics from both the pre and HT receiver to the amp that way if it would work better than a speaker switch
It's generally not a good idea to connect two line-level outputs together, even if you avoid having both components turned on at the same time. Depending on the particular designs it might work ok, or it might degrade sonics to some degree, or it might even compromise long-term reliability.
What would work well, if you want to use the same power amp for both purposes, is to insert a line-level switch to select whether the pre-outs of the receiver or the outputs of the preamp are routed into the amp. The DB Systems DBP-2JAU/5 ($110), listed near the top of this page
, would be a good choice. See the links just above it for the DBP-2J/5 for further info.
The other choice, as you realize, would be a speaker-level switch. I doubt that the line-level switch would have a perceptible effect on sonics, but I wouldn't be too surprised if a speaker-level switch did have a slight effect. Other opinions may differ. I did use that specific DB Systems switch in my system many years ago, btw, with excellent results.
P.S: Just saw JJ's post. Great minds think alike!