Can I hook up two amps to the same speaker?

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.

Rwwear, very cool. Looks just like what I need. I probably could rewire the interior (or have it done) with Ibis cable. That would keep the continuity/wire DNA in sync, don't you thin? One or two of those switch boxes? I suppose the binding posts are on the back? thanks for the tip. warren

You should be a bit intimidated. If you do this wrong, you risk serious damage to your amps. In addition, to what was said above, I've heard that some tube amps do not like having no load on the outputs while the amp is on. That would be a problem if you switched over to the transistor amp while the tube amp was still on. Yes, you might be able to find a shop to make up a switchbox with what you need. Or, you might consider putting dual banana recepticles on the end of the speaker wires and bananas on the end of the amp wires, put the ends in a handy place and hook them up like an old-time telephone switchboard operator. If you describe why you want to do this, there might be other and better solutions.