I would avoid that Sescom A/B box (the second one). It uses a DPDT switch to toggle the positive signals from each amp into the single output. But it ONLY toggles the + signals through the DPDT. It relies on common grounding all the input and output negatives. So what that means is you've got two amp input negatives connected to each other through the device. Essentially the unused amp negative acting like a signal antenna receiving the ambient RFI noise environment. Not sure the exact topography inside the box if its a star pattern or what-not, but at least a couple Amazon reviewers complain about ground loop noises. In a plastic enclosure like that its not going to be chassis/common grounded, so ground path and wire layouts inside would have to be perfectly equal between all channels. And even then, ground loop noise is tricky to debug because so much of it relies on the ambient noise environment of the user. One amazon reviewer replaced the DPDT switch with this
tripple pole dual throw and reported back positive results. This is essentially the same device-design I recommended in my previous post.
Thinking about it further, I
think (I am not positive on this mind you) a device like this with a 3PDT would need to be in a plastic enclosure. If you mounted it in a metal box, it would end up common grounding all the sleeves together... and thus partially negate the third pole on the switch.
Not sure about that first one... I would inquire with them if they use a DPDT switch and common grounding all inputs/output or a triple pole switch and isolated negatives between the two amp inputs.
Oh one more thing... that blue push-button switch I show in my pic is more commonly called a "stomp switch". Its designed for added robustness to be stepped / stomped on in a floor mounted device. Think musicians on stage, heavy equipment operators...etc. So its going to be more $$$ than a toggle flip switch.
