I have the 700BT and I bought a RCA-->3.5 and hooked up it to the Front Output cables on the din.

When I hook up my zune the music plays without the unit having control. I know the unit cannot search through my songs

by why can't turn up on the volume on the unit itself. Was plugging it into the front output wrong?

In other words, when I max out my zune...the music is still pretty quiet.

well you should be able to adjust the volume on the ZUNE for the level out and again on the avic for the level up, if it is turned up on the zune and turning it up on the avic doesn't get to the proper listening levels, then you may have a volume limiter set on your zune (this protects your hearing while using headphones)