hold down the audio button when the unit is on till it changes to a different screen. here u can really tweak the hell out of it.
2 down & u get more in your face sound, 2 up & u get more of a soft surround in the freq. that u want. for stock speakers i'd suggest 80 HZ maybe 1 down, but it all depends on the music your listening to. i used to sell these units, so i know them pretty darn well. let me know if you have any questions, glad to help any way i can.