High quality Speaker switch box for multiple amps?

I finally found a perfect solution for this problem. I tried the Mapletree Audio switch box, which admittedly is a little more elegant, but I did some A/B testing and felt like there was a loss of that last 5% of resolution and substance. I do have a very resolving system. I don't think the difference would be noticeable with a mid-level system.

I looked inside and I have to assume that the puny contacts and hook up wire do not do the job (even though they use a high quality rotary switch). So I thought about a hard connection to avoid small contacts and skinny wire. A simple, old school knife switch works best. I felt like I got that last 5% back. I tested two big copper 4PDT switches and this one has the largest contact area and the most copper where it counts: Tatoko Knife Switch Dual power Copper Power Disconnector Switch Semicircular switch 4P 100A https://www.amazon.com/dp/B07V5Z6GP7/ref=cm_sw_r_sms_apa_i_J-8yEbBBR32DH

Remember, if you have a tube amp you should have resistors in the circuit so that the tube amp is never on without a load. Not sure what the load should be. Do your research. I used the resistors that Maple Tree sent with their box. Btw, anyone want a good deal on that box? :) 

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). 

3 amps is tough.  I see this one for two amps into one or two speakers:

https://www.amazon.com/TC-7220-Amplifier-Selector-Comparator-Crossover/dp/B00LNOAGZQ

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

https://www.amazon.com/Niles-Black-FG00002-Auxiliary-Selector/dp/B00006I5J0

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

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

To make those Amplifier switcher safer for all Amplifiers, parallel all speaker outputs with 25 -100 ohm  5watts resistor.

This is a link to Van Alstine comparator as bugredmachine recommended:
http://avahifi.com/products/accessories/abx-comparator-switchbox
And it safe to switching bridged Amp.

Van alstine has a box that can switch all inputs and outputs and level match them. About $1500.00. 

Try this one:
https://www.amazon.com/Niles-Black-FG00230-Speaker-Switching/dp/B00W4FN47K
It switchs input and output of 2 amplifiers, 600W rated, but only for single ended.

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.

Looks like I would need to separate "boxes" for this. One splitter for the preamp audio outs and one for speakers