Sharing Speakers between two amps

I have recently built an analog system and am seeking a solution for sharing speakers with a surround sound system for the occasional movie night. I purchased a switch box but noted that it has resistors across the poles, apparently to protect the amps, and am concerned about their affect on the audio and have therefore chosen not to use it. I understand that using any switch requires careful operation with both amps off etc. Thinking about building my own switch assembly with properly sized components and wires etc. Would appreciate any suggestions or precautions. Really trying to avoid buying a 2nd set of speakers. (Rogue Cronus Amp and Denon Receiver)
Thank you.
Been looking for a foolproof solution myself.  If not done right........poof goes the amp or amps. Got no response on the forum here worthwhile. There are some true and tried swith box suggestions on the web I'm debating trying. But one error and you're done for. Maybe that's why no one chimes in.
You got it all wrong.

Take the left and right front outputs from the Denon rec into an analog input on the Rogue amp your main speakers stay on the rogue at all times.

To play a movie turn the rouge to the input you ran with the analog output from the Denon and raise the rouges volume to match the vol from the center then once the vol is matched use the Denons vol and you are good to go.

Dave and Troy
Audio Doctor NJ
What Dave said, otherwise you could just get a pair of smallish bookshelf speakers for your mains dedicated to your HT system if you have the space. Shouldn't worry about SQ too much since these are mostly for ambient sounds. Make sure your center channel rocks, however. (plus gives you a chance to buy new gear which is always fun)
I think Dave is settling on mediocrity.  You end up killing the theater sound by not having a seamless RCL with same amplification.  Also, you end up having an extra component into the 2 channel rig.
It's a compromise that I wouldn't be willing to make.
I know Niles makes/made an amp switch to do this.
Thanks Forum. Some suggestions I hadn't considered. Didn't realize that with 5.1 surround, the center channel was doing all the work. Buying a set of smallish L/R mains is a potential solution. Also like the aux input to Rogue amp using analog outs. Creative, even if not perfect. 

For gillatgh, I bought a switch from Amazon (Specialty-AV SP-71). Generally a well built unit with double rocker switches (L and R) with banana plugs and 16 ga internal wiring. My primary concern is that there is a 5W100 ohm J resister across each of the four amp inputs and I'm not certain what effect on sound might occur introducing this into the signal path. We place significant emphasis on speaker cables etc, only to insert a switch....I'm having second thoughts.

Can anyone comment on the true audible effects from placing a resister across amp outputs as a protective measure?