3 three channel system, anyone?

My Fisher tube integrated had a center channel power output in the 60s. You can do this with ANY preamp. Get 3 high quality Y connectors, male to two female. Plug one into the right channel and use one of the female plugs to run your regular interconnect to the amp, do the same on the left channel. Then run the ICs from the other two plugs to the third Y connector and plug it into your center channel amp. It carries a combined L+R signal. You are simply doing externally what the other preamps do internally and will have no more signal degradation than they do, assuming high quality connectors.

Meridian uses and older system called Trifield to accomplish this, it used to come on Yamaha receivers back in the day too, it works amazingly well, simply making a center of the left and right would be silly in my mind but YMMV....

What do you think the center channel is but a combination of the left and right? This is how it was done in the days when 3 channel was common.

Stanwal...If you use a simple Y interconnect you have shorted the Left and Right together. ALL channels will be Left plus Right... in other words Mono. To mix Left and Right so as to get a center signal without screwing up the Left and Right you must use a resistor network.

In my opinion the simplest and best way to drive three front speakers is to use a stereo power amp with the signal of one channel inverted. Bridge the amp with your center channel, and reverse the speaker wires on the channel that you inverted. Your amp will see a low impedance load, but I never had a problem even with 4 ohm speakers.

Another way is to connect the three speakers in a Y configuration. This will not lead to a low impedance load,

Many years ago I experimented with non-standard connections for speakers.
Using 2 amps I had a standard pair of L/R speakers in front using the first amp, my brothers SAE. No problem.
Next, I connected a pair of speakers IN SERIES between the 2 hots of another amplifier. These speakers I stuck in the BACK of the room, maybe 10 feet apart. This amp was my Kenwood from my first 'serious' effort at better sound. The effect was startling. Any music with phase information 'intact' sounded really live. As a matter of fact, albums recorded live were scary. The music would come from the front pair, with little or no sound from the back. As soon as the crowd began clapping, you were in the MIDDLE.
Current over-engineered music lacks many phase cues which renders this probably a moot technique and makes my absolute phase switching on the amp so much extra circuitry.
OH, the technique to which I refer? I got the idea from SQ / QS 'matrix' sound at the dawn of '4 channel'. I think Dynaco (?) sold an adaptor which did the same thing, from a single amplifier.