Bought my car about five years ago, it had some decent car audio already installed. Never bothered about setting or anything until now.

Sitting in my VW golf 5 is the following :

DLS UP36 3-way speaker system
DLS Ultimate A6
2x12 " Cerwin Vega MAX12 subwoofer not sure but I think it's these
2x JBL GTO 2000

The plan is to upgrade to get a better sound quality sound (think its called SQL around here).

From what I've heard cerwin vega is kind of a SQL/disco heavy bass subwoofer.
So I think about changing subwoofer to something else, 2x8",1x10" or 1x12"?
As Im used to 2x12", I still want a subwoofer with priority is SQL, but still being able to get some nice bass feeling.

Heard good things about a sub called Gladen SQX 10 VB High-Performance.

And headunit I think about getting either Alpine 178BT or Pioneer DEH-80PRS.
Some people saying alpine is the best, while others say pioneer.. No idea here what to get.

What would you upgrade if you had around 600USD? Live in sweden, so probably will have a hard time getting subwoofers made over there..

PS. I really not into this, got no clue about settings, and such.. Basiclly my dad bought this car 6years ago with the audio already installed. 1 year ago I bought it and most of the time I've been happy with the disco-heavybass sound. Also quite satisfied while listening to pop/rock/ambient/all kinds of music.

But Im done turning volume to max just to make whole car vibrate :P