Kinda curious.

I'm trying to get the best sound out from the stereo

I have a cassette tape which connects the 3.5 mm headphone jack to my mp3 devices (my phone).

So what do you guys keep your bass/treb/etc at?

I also find the cassette player more loud than via FM.

 

Bass-5
Mid-3
Treble-4

This usually sounds great as long as what I'm listening to is good quality.

When you use the tape adapter for AUX try playing the music at half volume on the device. This way it won't distort the music. < I used to do it that way till I added an input for the iPhone. If I left my iPhone on full and turned up the car radio, the audio would become distorted. With the iPhone volume half-way up, and the stereo cranked up, the music was still pretty crisp (not cd quality, but good nonetheless).