Is there a 30pin in/out device that improves sq of iPod touch/iPhone, not aux out

Looking for something to go in between a iPod touch or iPhone and my headunits using the 30 pin connector for both the input and output.

I know Fostex has the hp-p1, and that uses the 30 pin for input, but an 3.5 aux for the output.

I don't mind spending money to improve the sound quality, especially below 50hz. I searched and found that Memphis has the bass 2.2 that works like a preamp, but I'm hoping to find something that is moveable. And I can use in the car, or with other devices I have that use the iPods 30 pin for audio input.

Or does anyone know of a way to improve the 50hz and below output on these devices.

I know in iTunes I can change the compression and that will accomplish what I want, but I haven't bought a cd in 5 years, all my music is downloaded right from iTunes, so that doesn't help me.

Thanks