well with a eq you can use a rta and pink noise and set respocne to be generally flat and smooth so things are spectricaly balanced. Than a fine toune to taste after a basic rta ajustment.
for best results use a 30 band eq but takes a pro to set it for you. For just a basic settings some in dash 1 oactave (9 band) units can do pretty well.
It all depends what you want and how well your speakers can perform.
A lot of newer CD players have decent EQs built in for everyday use...they beat the old bass and treble controls //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif