radio help

I have a Pioneer DEH-6400. When I connect an amp and sub, I loose out on my rear speaker. Did anyone else hear about this problem. I was told that the sub out share the rear line, so I have to sacrifice the rear speakers when adding a sub. Is there a way to fix this? Does anyone know if the DEH-P7400 does this too?

This is weird, are you using RCAs and a remote wire?

I'm confused. I mean yes the 6400 only has 2 pairs of preouts. But question is are your rear speakers hooked up to an amp? I don't see how hooking up a sub can do this. I never did like HUs with only 2x preouts, but then again not everyone needs three pairs. It depends on how your going to setup the system. Anyways, give us a little more info on your problem.

I'm using the rca and turn on wire. The 4 speakers in the car are connected to the radio. Only the sub is on the amp. I bought the HU at Futureshop and they told me it's a problem that pioneer has because it doesn't have an independent sub control. They offered to exchange my radio for the 7400 model. It also has 2Xrca, so I don't see how it would change anything. Any help?

Yeah it sounds as if it's an internal problem. Cause thats not normal. I would switch to the 7400. Or if you can get your hands on the 7300 (last years model), it has 3 sets of preouts.