I am looking for a user manual

use from here
Pioneer DEH P480MP User Manual

I am looking for the Hybrid Professional Mixer MX3206DU user manual.

follow the link below for the user manual directly from pioneer.

http://www.pioneerelectronics.com/pio/pe/images/portal/cit_11221/93198953Operating%20Instruction%20VSX-D914-K.pdf

Series the speakers, they may not get as much power as you would like, but your receiver will last longer.

The slider or the amps for channel 1 may have a problem.

Sliders do wear out.

Try shorting channel 1 input and see if that affects the noise. A hissing noise is probably a bad preamp chip. That is shop work at a repair facility.

Rear Surrounds are not supported on this unit, they would be the 6th and 7th channels in a 7.1 rig. I think you mean Surrounds (channels 4 and 5 in a 5.1 rig).

Lets ponder: How is there any relationship between Surrounds and your separately-amplified Subwoofer? I don't see it, unless you inadvertently chose OFF for the Sub definition when you were in the Speaker selection menus adding the Surrounds. Look again.

Looks like a scanned version of the user manual is available on
http://www.pioneernz.co.nz/Site/Pronto/Files/user_manuals/SX255R%20USER%20MANUAL.PDF

good luck to those who have been on this post

Be sure the sound source has a center channel output ie. not a 2 channel source only, try the test tone setup for 5 or 6 channel balance, if no sound from the center channel still then it is looking like maybe the center channel is blown.

Yes. It is 5.1 surround. There are 2 front channels, 1 center channel, and 2 rear channels which comprise the "5" in 5.1 surround. The pre-amp output channel for a sub is the ".5".