wired modulator for mp3 player

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Hi.

I'm shopping for a wired modulator to connect my MP3 player to the car
audio system without auxillary input.

Wired modulator seems like the best option, but I'm having difficulty
finding a good one.

Requirements:
automatic antenna-cut off
good sound quality
automatic on/off switch ?

I found some modulators from no-name brands like Xo-Vision, Pyle,
Acoustik, etc... but have no idea which are good and which are crap.
There also no reviews on the net.

Any suggestions ?

Thanks.