Bryston 2WSB switch box to choose amp that drives speakers

Good catch about the commonality of the red terminals, Treynolds155.

There are some circumstances in which that switchbox would work ok in selecting between two amplifiers if all of its red terminals are treated as black and vice versa. But I wouldn’t feel comfortable doing that with your Threshold S200. It’s manual, which I found at HiFiEngine.com, states as follows, in reference to the S200’s speaker outputs:

Each channel’s output connector consists of a red and a black post on a common base.

These outputs, should be considered as electrically isolated from the chassis and from each other. In the case of dual channel amplifiers there should be no direct interconnection between the output terminals of the two channels under normal operation. Connect the output terminals of each channel only to the loudspeaker, not to each other or to anything else.

I would infer from that that the black output terminals of your two amps, as well as their red output terminals, should not be connected together.

Other conceivable issues are the power handling capacity of the switchbox, and whether the switch is break-before-make or vice-versa. If the switch is make-before-break, when changing its setting the two amps would be connected together for a brief instant, which conceivably could be a problem if either amp is powered up at the time.

Best regards,
-- Al

Here’s a basic selector,

https://www.russound.com/products/connectivity-and-control/speaker-selectors/dual-speaker-dual-sourc...

You could also look for a Niles SAS-1 or a Niles SPK-1. These are no longer available new but can be found used. They would offer options for switching automatically.

As I posted this, I just noticed Al's post. Hopefully he will see my post and comment if my suggestions are suitable.

Niles Spk-1 switch both positive and negative, the 12v trigger is set and forget.
http://ww.nilesaudio.com/product/speaker-level-b-switcher-12v-triggered-FG00240

Al I really appreciate your looking into to this to that degree! This is really quite maddening that there isn't a quality switch that can accommodate it. I mean really I'm just looking for a four pole double throw switch that won't muck up the sound. I'll end up making something if I have to.

Thanks for the links guys...I'll check them out.