Help with Amplifiers-to-Speaker Switch Design

My main lockdown project has been re-working my audio center. The end result will allow several speaker amps to be up and running at the same time. Floor space is more limited so I'll usually have only one set of speakers out front. How to switch them between the amps?

My initial design called for several sets of speaker cables, each connected to one amp, connect the ‘correct’ cables to the speakers with banana plugs. But even before the project is finished I'm tripping over multiple cables coiled up or laying all over the floor. And the amps need to be turned off when not connected or they can short out or be damaged due to no load.

I woke up this morning thinking about an amplifier switcher. My main design goals in order of importance are 1) don't blow up my amps or speakers; 2) keep the circuit simple to avoid sonic degradation; 3) ease of switching ; 4) ability to leave all amps up and running when switched to "off." Why the last? Because I'm lazy, And I'd like to compare tube amps to each other while they're at running temps.

I drew up the following design:



A four pole, dual throw switch shunts each amp between a dummy load ('Off') and a common set of cables to the speakers ('On'). Eight-ohm 250 watt resistors are used to load the amp when in the off position (that value resistor only because I happen to have a lot of them lying around right now.) Each amp gets its own switch and resistor set. A physical guard on the front of the box prevents more than one amplifier from being switched on at any one time and forces all others be off before switching one on. This drawing shows 2 amps connected but I could theoretically add more.

I think this hits my design goals if I use a quality switch and connectors. Anyone see anything I forgot? Any way to further simplify this or reduce the number of resistors without endangering the running amps ?

 

https://www.amazon.com/TC-7220-Amplifier-Selector-Comparator-Crossover/dp/B00LNOAGZQ

same folks in Taiwan who make the TC750 phono pre, they have good ears. I dont use this amp switch but I do hve their TC7240 line level switch and its very very good, sonically and build wise.

 

I looked at that and several others, I think that's probably the highest quality one I saw. The issue with it and all the others is there's no load on the amp when in the 'off' position. That's fine for solid state but most tube amps can go 'boom' if run that way for long.

I think its a cost issue, big resistors aren't real cheap & there's not a lot of demand for this type of thing.