im slightly confused, by RCA, you mean remote wire yeah? (the thin blue one?)
if the amp light comes on the remote wire is fine, or at least it is for now!
and the two preout adaptor, how does that work? does it run off your standard speaker wires? this sounds like it is causing you your problems.
its doubtful, although not impossible that a new set of phonos will solve your problems.
are the phonos new? if so another set will definately not be the way to go.
sorry i couldnt be more help, hopefully someone will be able to help more.
have you thought about getting an aftermarket stereo? they are a lot easier and more reliable to add stuff too. has your car on dash computer features built in? ( mpg + fuel left ect.) if you use these features often you may be reluctant to lose them but my last car had and i never missed it when i fitted my stereo!
depends how much you use them though.