"Y" Connector: Can Split A Signal How Many Times?

Do you think this would work without much signal degradation?

I think that will probably be ok.

I'd suggest Blue Jeans LC-1 interconnects, which have very low capacitance, as well as low price. That should result in cable capacitance being a non-issue, given the 18 feet or less total of the lengths, and the fact that you apparently will be using a solid state pre-pro.

When you determine your tentative choices of pre-pro and amps, let us know their make and model, so that impedance compatibility can be confirmed.

Regards,
-- Al

Why not use 3 pairs of speakers and an impedance matching speakers selector box? This way, you only need one stereo amp, and don't have to worry about "Y" adapters.

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Pixel, I want each speaker to have its own discrete amplifier channel. A stereo amp powering six speakers doesn't appeal to me.
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The price of the interconnect is irrelevant. You need to tell us the output impedance of the preamp and the input impedance of the amps as well as the current drive capability of the preamp.