Can I hook up two amps to the same speaker?

Elizabeth, are the switchboxes required to use as a safty feature in case both amps are left on? If one amp is off why would their be a problem connecting both spades directly to the binding posts of the 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.