After browsing around on Pioneer's website, it seems that the majority of their amplifier product line contain high level inputs. So you could just hook up the amplifier without the use of RCA if you really want to go that route. However, you'll be sacrificing sound quality.
Colin has a point. You could use the low level outputs from the factory deck with a little work, if you're dead set on keeping the factory deck. You could also you a line driver off the factory deck to boost your factory head unit signal.
If you were open to replacing the deck for a minimal cost, I would go that route! You won't be disappointed and a lot of users on these boards have made some excellent recommendations without burning your finances. The factory head unit sucks.
