I installed a Rockford Fosgate 6 disc CD into 2005 Nissan Frontier, but with the voluum tune to max it has very low sound.

Recheck wining setup for proper connection

No. You replace the stock amp and substitute the new one in its place.

tough one i have no clue

may need to be cleaned get a cd lense cleaner and run it.

Are your rear speakers smplified or ran directly off of the radio?

i have the same problem. it started today. any luck in finding a solution?

you need to call sirius radio.I had the same problem with my XM.i called and they fixed the problem.

I have the same problem with the 2006 sentra

The CY108 is an original equipment stereo for the Nissan Sentra.
The manual for that should be available through your local Nissan dealer. Here is a link to Rockford Fosgate manuals. Just scroll down and look at a few of them. They might give you a clue as to how to operate yours. I hope this helps you.
http://www.rockfordfosgate.com/library/documents.html

if is there a warped CD in the tray
pull the unit apart


or a major fail .. easiest fix is
source a used Rockford Fosgate 6 CD player that works
plug that in
ebay / inline or wrecker 2006 Nissan Xterra Rockford Fosgate AM FM Radio 6 Disc CD Player PN...