Re: 2 into 1 speaker switch (or crossover A-B switch-over)
I'd be very careful indeed about this. If both amplifiers should be on and you switch between them there could be a momentary connection of the output of one amp with the output of the other. Even if you can be sure that only one is turned on, and one turned off at all times, the 'off' amp could load the 'on' amp.
Personally, I'd select a "break before make" switch to be absolutely sure that the two amps cannot even momentarily be connected together. If I were making this - and I have, but in reverse - to switch one amp to two speakers - I'd use gold plated relays with chunky long-life contacts. Then you can operate the relay using just a cheap switch (like the one you suggest) because the audio won't be going through the cheap control switch, only through the relay's gold contacts.
Found the picture of my relay switch-over box. To explain .....
This was taken during the development of the C7ES3. I had developed two different crossover circuits designs pointed out with the orange and green arrows.
On paper, and by casual listening (involving a lot of plugging and unplugging, many minutes of no-sound then sound again - absolute madness when making critical risk-the-business decisions) I couldn't reliably say which circuits I preferred. So I made the Instantaneous A-B Switchover Box Mk3 (in yellow ring) and hooked up the two pairs of circuits. Obviously, listening in stereo with two speakers, I had to make two 'orange' circuits and two 'green' circuits and switch the left and right speaker cabinets between either the two orange or the two green. So, at my command and with no (detectable) break in sound, I could settle back in the hot spot with a cheap foot switch (blue arrow) and flick between the pairs of circuits listening to my favourite music. The differences were subtle, but there was a definite winner to this instantaneous A-B comparison and that's the circuit I went with. The differences were so subtle that even with an instantaneous no-break changeover between the circuit candidates it took many hundreds of change-overs until I had a definite opinion and then days later, preference. If I had relied on my audio memory (mine almost non-existent) as I believe many so called 'audiophiles' would have, I may as well have guessed: it would have been no better than the flip of a coin. Why do 'audiphiles' put such ludicrous self-belief in the hearing when I, a designer, dont?
What you're proposing is in fact the concept in reverse: one amp driving two speakers, so the very same circuitry will do the job.
Total cost: about $20 plus about 3 hours assembly time. Every serious listener who respects his reputation should have one of these.
Hope that helps.
Alan A. Shaw
Harbeth Audio UK