Can I do this without hurting my system?

Okay, I finally received my Adcom amp. The Rotel is going back downstairs to my main system. What I'd like to know is if I can hook both my amplifier, and my receiver up to my speakers at the same time (there are 2 sets of terminals on the speakers). I have no intention of running both the amp and the receiver at the same time, but I do want to be able to quickly compare the sound of the receiver to that of the amplifier.
Also, the lady would prefer to just have to turn on the receiver to watch a DVD, and not have to worry about the amplifier (she is intimidated by these things).
So, can I run 2 speaker cables to each speaker, one from the amp, on from the receiver without any negative effects? While I'm at it, can I use both my receiver and my amp to drive the speakers at the same time? Thanks.

Those two terminals on your speakers are meant for biamping. To do this you would need to remove the jumpers between the two terminals on the speaker. If you do this, then yes, both amps can be on simultaneously. In fact, they will have to be. One will be driving the bass speaker and the other will be driving the remainder.

But, hooking up both amps, even if both are not powerd up at the same time, without removing the jumper could very possibly cause expensive problems.

Yeah, somehow I thought you were going to tell me that. Now I'm wondering if theres any very quick way I can switch amplification sources to compare the sound differences (if any) between my Adcom and Yamaha without damage. Maybe I'll just have to wait for my new banana plugs to arrive and do it the old fashion way.
Thanks again.

If you hook up both amplifiers to the speakers at the same time, you run a real risk of severed damage to one or both amplifiers. My advice is don't do it.

Believe it or not, there is a way you can easly switch between amplifiers. You can purchase a four pole double throw switch or (two) two pole double throw switches and wire the speakers to the switch legs. Electrical standby and emergency generators are wired to loads this way for switching to alternate sources of power. If you know what you are doing and are careful, there should be no problem. If you do not and make a wiring mistake....pfffff, goodbye amps. Short circuiting the two amplifiers together even momentarily by accicent will ruin your whole day.