Bryston 2WSB switch box to choose amp that drives speakers

I really want to be able to choose between a low power amp for tv/background music and my good amp for serious music sessions. I'm tired of amp rolling, have posted recently about this and got good advice not to use two sets of speakers cables but only one live amp. So I'm thinking of a device like the Bryston, but have the speaker outputs be the amp inputs and the amp input be the speaker output. As long as only one speaker is selected at a time...electrically that should work. My only concern looking at the schematics is that the red positive leads are wired together and the black negative leads are switched. Could this still cause voltage to be applied to the unpowered amp? If so would swapping polarity work? There's a schematic on this page.
Any help on this would be greatly appreciated.
This is only for switching between two sets of speakers. I have one made by Adcom. Never known of one like you describe. Are you afraid of wearing out your SS amps? Just switch by hand! The exercise will be good for you!
LOL I could use more exercise but I switch back and forth so often that it's a real pain in the arse, to the point where often I don't even bother connecting the good amp. The reason I do this is because the good amp runs in class a, so it's very hot and draws a lot of electricity, plus its a vintage Threshold that I want to limit its use for music only. I can't justify watching the news or football with it in the audio circuit. I could just use the tv's speakers for that but I also like the little amp for background music, I'll leave it on all day while coming an going. I won't do that with the Threshold. 
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, 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,

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.

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.

First, a couple of corrections, with respect to the Bryston switchbox:

1) Ignore my previous comments about make-before-break vs. break-before-make. I hadn’t noticed that the Bryston unit provides a separate and independent switch for each of its two signal paths.

2) Bryston’s setup diagram that is shown in one of the photos at the link provided in the OP states that it is the black binding posts that are common to all inputs and outputs, which of course directly conflicts with their schematic that is also shown.

In any event, per my other comments I would rule that device out.

I can’t tell if the Russound switchbox Tony (Tls49) linked to would be suitable, because there is no indication as to whether or not it switches both + and -. Also, if the impedance of your speakers is in the vicinity of 4 ohms your S200 amp (rated at 100 watts per channel into 8 ohms) might be a bit too powerful for it, given the 150 watt power handling spec of the switchbox.

Regarding the Niles SPK-1 both gentlemen referred to, if I understand correctly it is designed to be switched by the switched AC outlet of a Receiver or other component that it would be used with. If neither of your amps provides such an outlet that may be an issue.

Perhaps a look through all of Niles’ switchbox offerings would prove useful, if you haven’t already done so:

I did take a quick look through the various pro-oriented switchers that are carried by B&H Photo Video, but everything I saw there had some combination of uncertainties, involving power ratings that would be marginal at best and/or whether or not the unit switches both + and -.

Best regards,
-- Al
Thanks again Al for really digging in there to help out!! I think there's two versions of Bryston's switch so that may be the difference between common + or - rails. Regardless...probably not safe either way. I looked at Nile's site and their DPS-1 specifically states two amps switched to one pair of speakers but nothing specific about both +/- being switched and it sounds like their binding posts are anemic so probably not the quality I'm looking for.  

I'm starting to think a custom one is the way to go. I found this four pole/double throw on/off/on switch:

All I'd need is a project box and some Cardas binding posts and wire. As long as the switch wasn't noisy it should work great. Thoughts?

Looks perfect. Nice find!

Also, Digikey sells it for a somewhat lower price:

Best regards,
-- Al

P.S: Keep in mind that if the lower powered amp happens to be a tube amp that has output transformers, it should not be operated without a load connected to its outputs, especially if it is being provided with an input signal.
I can confirm that the Niles SPK-1 switching both +/- terminals by using two 12V DPDT relay rated 8A @ 250V internally. The 12v trigger can simply use a 12V DC adapter.
That's a great price Al. I like that it has an off position in the middle, no way for the two amps to be mixed. This whole thing may seem crazy to some but I'm really looking forward to being able to just flick a switch for what amp I want to use. 

I'll post pics when this is built, I've updated my system pics for my recent updates. Pales in comparison to a lot of the systems here but she's mine and it does sound real good...especially when the Threshold is in play. 

Thanks for all the links and help guys!!