Can I hook up two amps to the same speaker?

If you leave both amps connected to the speaker, the one powered up will likely damage the output stage of the one powered off. That's why you need a switch.

Also, if either amp uses tubes in the output stage be sure that the speaker is connected to the amp before powering up or you could damage the output transformer. No such problem with solid state outputs.

Ghostrider, I understand now the reason for the switch. One of my integrateds is tubes. Wouldn't you hook up the spades with power off for safty, anyway? Once the tube integrated is hooked to the swith box, powering up is not a factor, correct? It would seem that this, once the deed is done, to be a good way for me to have tubes and ss. I'm a little concerned that the switchbox is a kink in the signal--amp to speakers. Am I over reacting?

May I add that the switch you seek should have a 'break before make' not the 'make before break' type circuitry.
Here are the make before break/break before make definitions:
In a make before break type, a contact will not open it's primary output circuit until it has closed it's secondary circuit. Conversly, in a break before make type a contact opens the circuit to one output before it closes the circuit to a second output.
Also a DPDT with a "OFF" center position will work.

This electrical stuff is a bit intimadating. Would it be possible to find an audio repair shop to construct the two switch boxes with binding posts, etc. for me. Then all I would have to do is hook up the speaker cables? I could call Zu and get a few feet of their Ibis cable. Would that be cool? Maybe a bit more expensive, but less heatburn.

You can get an automatic switch from someone like Niles Audio for this exact purpose.