Balanced switch for preamp output

Plenty of cheap switches out their that I’d avoid. Years ago Wireworld made a RCA switch called the Wireworld Comparator. Probably would not be hard to build one with quality parts or contact the big boys such as Kimber, Wireworld or even Chris at VH Audio who might be up for building you one that will not degrade anything. Others to reach out would be Michael Percy if he’s still in business or Parts Connexion.

For manual XLR selector,  check out the Goldpoint

https://www.goldpt.com/sw2x.html

If you want 12V trigger XLR selector, there's an Australia made ARX RS-1 remote switcher

https://probroadcastsupply.com/arx-rs-1-remote-switcher-stereo-xlr-balanced-remote-controlled-switcher-arx-rs-1

Why do you need a switch? Your preamp has two pairs of balanced outputs. You can connect both amps to the preamp, and simply power off whatever amp you're not using.

I'd bet Ayre could make a switch for you. There is a new guy, Jake Forsyth, who is answering tech calls. 

Ayre is pretty good at adding mods to their equipment. I know they can add a high pass to their amps in order to use Vandersteen subs. You just have to ask. ( And, usually, the price to convert is very reasonable).

Bob