When using the Bose, I have always used the summed output, using one cable. However there are times when there is no indication of L/mono e.g. I have a dual 1/4 in TSF to 1/4 in TSF Y cable(Hosa YPP 111), and wonder whether to use it, or a mixer panned hard.

Of course you are not going to get stereo from one Bose, regardless of the hookup. I would test the various ways and use my ears to see if one sounds better than the other.
The few times I did it, I ran from left and right outs from the keyboard into the stereo inputs on the Bose Compact. Korgs sounded fine, Yamahas not so fine. Yamaha arrangers NEED stereo processing to reach their potential.

Hi Bernie,
I ran several tests with one Bose using just one cable into L/R and then the Hosa Y-connector.
On certain styles certain guitar parts and/or certain drum parts did not sound right using one cable. Something was missing or the volume was to low.
Using the Hosa Y-connector does not give me stereo sound, but it makes the sound on the Yamaha KB fuller and more even. No parts are missing now
Hope this helps.
Eric

Different setup but same situation .If I'm only using one of my JBLs which have a three channel mixer in them I run two cables from the keyboard and plug into two channels on the speaker.
Everything goes thru my keyboard so I don't need to run anything else into the JBL.

Stereo always..... two speakers ...

Bernie I to labor over the same thought; There is a right and a left but no combination output. I used a Y- connector to correct the problem. As Eric said, you lose part or all of an instrument.

All my keyboards have a combining output L/R. Which one of your keyboards does not? Is it Yamaha?

I gave up on stereo a long time ago. My Opinion: the people in the center enjoy the stereo sound. The ones on either side do not get the full sound. I often, when needed, edited the panning of each instrument and placed all the instruments in the center to overcome the stereo effect. The Y- cable seems much easier.

John C.

The main reason is best to use 2 Compacts or 2 of wherever PA system you may use...
Is because Yamaha use Stereo Samples, Not Mono samples.
Mr. Mason is correct.
I use a Tyros 5, (That I recuperate from a little "incident")
but, now everything is perfect.

Thank you one and all for your input. I have learned that the kb in question(Pa4X) allows you to either one for a mono signal, hence, the question regarding the Y connector is moot.