Switch needed for one pair of speakers and two amplifiers

I inherited a pair of truly magnificent Tannoy D700 speakers which are currently bi-wired as the main stereo pair (and Sub!) to my Onkyo TX-NR609 AV Receiver. They perform wonderfully well in this role, especially with a second pair of smaller Tannoy dual-concentrics as the rear surround speakers.

Although the Onkyo is a fine AV machine, it can be beaten when listening to music by a good stereo amplifier, and I inherited one of those too. Currently out of use is the heavyweight Technics SU-V90D, a class AA amplifier which used to be paired with the Tannoys before they came to me.

I would very much like to wire in both amplifiers to the D700s so that the Onkyo can cover AV use and the Technics any stereo demands from my Cyrus CD8SE CD player and Thorens TD150 turntable. Then I get the best of both worlds.

The Technics cannot manage bi-wiring so I would be looking at taking just L&R channels from this into a switch of some sort.

The Onkyo would send 2 x L&R to the switch.

The switch would then completely isolate each amplifier from the other - and yes, I will be careful not to power on either amplifier with effectively no speakers connected.

Does such a device exist or am I going to have to construct something?

There are plenty of switches which select different line level sources, but I need something rather more robust than that. And there are switches which will cope with a single amp and multiple sets of speakers. Unfortunately I cannot find anything to cope with my (proposed) configuration.

Thanks all,

Martin