I've set my fade to about 80% forward so I don't blow the speakers. I don't know what the rollbar speakers are rated for but I figure that's the safest way to start off. Chances are they work fine with your head unit. The headunit isn't overly powerful to begin with. You might want to consider that as a starting point however and work out from there.

 

I'm running a cda-9857 with the fader on 2 or 3, depending, and the rear speakers are fine. during testing I left it at 0 and played it at fairly high volume with no problems.

The speakers aren't great as far as sound quality goes, but they can handle HU power fine.

 

Sorry to bring this post back from the dead, but it is my understanding that the roll bar speakers are on the front channel, and there is no rear channel? Is this all assuming that the roll bar speakers have been re-wired to the rear channel of a HU, or is there in fact a rear channel already?

 

On 06+, the roll bar speakers are on the factory rear channel. You can roll the stock fader all the way back and listen to nothing but the roll hoops if you want.