How to deal with only two pre outs on aftermarket stereo

I'm thinking of buying a Bluestate RA-558 for my 8P A3 with Bose as it has DAB and Bluetooth built in.

But it only has two RCA Pre outs, the Bose needs 4. Can I just split the L and R pre outs in two so the front and rear get the same signal?

Thanks for the reply.

I do have a Blaupunkt Woodstock DAB 54 at the moment but I've had to put in a bit of a lash up to connect a CANBUS adapter for the Multi function steering wheel and separate Blaupunkt Bluetooth adapter for hands free all through the Quadlock and I've got quite bad engine noise interference. A local audio shop tried a Ground Loop Isolator on the pre out, which made no difference, and reckoned that the stereo might be faulty; some sort of protection circuit for the pre outs might have blown. I'm worried that the multiple connectors might be the problem, DIN to phono pre outs to quadlock adapter, DIN Y adapter for the Bluetooth and CANBUS, and the various power leads floating around for the aerial, Bose, Bluetooth unit and ignition.

If I can get the Bluestate with Bluetooth and DAB then I can at least get rid of part of the lash up, I'd end up with better quality than I have now. I could get an ebay Blaupunkt Nashville but might end up with the same problem if it's the wiring.

Thanks again.

They've definitely used the pre outs because I bought and supplied all the leads for the first installer and watched the second shop try a Ground Loop Isolator in them. So there's a DIN (C1 yellow connector) to 4 RCA sockets lead (shielded) (PC3-11), that's connected to a PC9-416 Quadock Adapter RCA plugs (also shielded).

Then there's a Blaupunkt Bluetooth adapter and Blaupunkt CANBUS adapter both connected to the stereo (using a Y adapter for the green C2 DIN socket on the stereo) and manually by me to the correct pins on the rest of the PC9-416 Quadlock adapter:

Autoleads PC9-416 - Audi A3, A4 Active System Wiring Harness Adaptor

I'm away at the moment. When I get home I'll check out the ground and I'll try and feed an audio signal from an mp3 player into the pre amp connectors to see if it's the wiring or stereo causing the whine.