Any one using 2 separate amps using a/b switch to same speakers?

You're likely seeing mono block setups or biamping configuration when you see multiple amps. Every time I thought about swapping in a tube amp with a SS amp using a switch I had visions of blowing something up.

One of the problems with a switch is that it can introduce an unwanted/additional sound artifact. Unless you are a dealer that needs to switch between different amps/speakers, it would be better if you just re-cable each amp separately.
Probably not what you wanted to hear, but I had to say it.
B
PS- I own both SS and Tube. I use the tube amp in winter and SS during summer months. It's nice to change things around.😉

I was in a similar position a few years ago -- wanted a switcher to change between a tube and a solid state amp.  One of my preferred dealers, who's opinion I give weight to, said that there was no way to do it without degrading the sonics.  I never took steps to confirm that and just stuck to switching out speaker cables when I switch between amps.  However, both amps are hooked up to the same preamp, so no cable switching there.

Good points. My pre does have two amp outputs, however, the second goes to my sub.  Switching out rca’s And Bananna plugs are really not that big of deal. 

You might try a TC-7220 2-Way Amplifier Speaker Selector Switch Switcher Comparator 

I am pretty far down the Audiophile food chain but,I use it to select between a Primaluna Prologue 5 and Emotiva XPA-100[x2] amps.

Niles Audio SAS-1
To be caution most tube amp and some SS amp will damage without load.

IMO the Niles gear is not all that great - lots of noise and potential for damaging your gear.  FWIW I wouldn't use one for any valuable gear.

You don't mention if you are using a preamp or integrated systems.  If you are using a preamp the ideal way to do this is if your preamp supported more than a single output.

If not and you really want to do this I suggest that you look at the Luxman AS-4III or AS-44 RCA switchers.  It's very good and is not too expensive on eBay from one of the reputable Japanese sellers.

You can also do this a different way, via speaker outputs.  The Luxman AS-5III, AS-50R (remote) and AS-55 are very good products, as are all things Luxman.  I own an AS-50R that I use for comparing speakers and it works great.

You might also look for a used Manley Skipjack RCA switcher.  This was probably the best unit of it's type but it was sort of expensive.  They occasionally come up for sale used but they tend to go quickly.

You might also look at AVA ABX Switcher, a one box solution.

https://avahifi.com/collections/accessories/products/abx-switch-comparator

imahififan, that looks like a great solution