oz_orion,
Generally with FM modulators, you do lose some quality due to the limitations of the FM bandwidth.
If you definately want to go down this track, id recommend the alpine stacker and fm modulator, you will get better sound quality from one of these than a cheaper brand.
You can get stinger adapters which will make the steering wheel buttons work with most headunits that have a remote control function, however this is around $250, combined with a head unit ($300-$400). It depends how much you can pick up a stacker and fm modulator for.