High quality Speaker switch box for multiple amps?

Stupid idea, I know. But if I wanted to have 2 or 3 separate amps (NOT running at same time, of course) to choose from with 1 preamp. Is there a switch box (preamp to box, box to multiple amps with a,b, c switch, box to main speakers) that is of high quality and will have very minimal effect on sound? Of course I would keep same brand/model of speaker cable at all points. Just curious
Looks like I would need to separate "boxes" for this. One splitter for the preamp audio outs and one for speakers
You would have to build a custom box. I recommend Grayhill switches if you want something that won't completely destroy the sound. You'll pay a bit for one but they are some of the best for something like that.
Try this one:
It switchs input and output of 2 amplifiers, 600W rated, but only for single ended.
Van alstine has a box that can switch all inputs and outputs and level match them. About $1500.00. 

This is a link to Van Alstine comparator as bugredmachine recommended:
And it safe to switching bridged Amp.
To make those Amplifier switcher safer for all Amplifiers, parallel all speaker outputs with 25 -100 ohm  5watts resistor.
if testing, you could also try running one amp into each speaker and using the pre-amp to "switch"

this won't test the sound staging and some other things, but costs nothing
Regarding a line-level switchbox to go between your preamp and the two or three power amps, and assuming that all of the connections involved are single-ended (i.e., RCAs), I’ve had good results with the DB Systems model DBP-2JAU/5 ($110) listed near the top of this page. I've used it in a couple of different 2-in / 1-out applications, but it can also be used 1-in / 3-out among other ways. It is similar to the DBP-2J/5 for which a review and description are linked to, except that it has gold-plated jacks. For contact information go to their home page.

Another possibility, although it costs $359 plus options, is the Decware Zen Switchbox.

Good luck.  Regards,
-- Al
3 amps is tough.  I see this one for two amps into one or two speakers:


I would use this between the preamp and amps (unfortunately, no longer made but can find used):

FWIW, I've had a standard Decware Zen Switchbox for a couple of years now and find it to be completely transparent when using it to add sources to my 1-input-only "integraged" amp(s).