I'm the proud owner of a Forte Koup SX 2.4l /AT and I must say that the sound in this thing is incredible

ok I'm not in my 20's anymore trying to pop the windshield off of the frame but it is plenty for my taste ,never passed the 20 out of the 30 sound level

I'm sure the Sirius Sat radio makes a big difference (digital)

and of course the obvious, everybody is different and perceive music in different ways , but it comes to the point, that since I'm no pro(just like most of us) when it comes to sound quality , I feel that the stock system is plenty for me,
good power (watts) ,4 adjustments for the Bass,which is more then enough to blow your ear drums off , some descent Tweeters and speakers (what ever they are 6x9 or.........) so until you actually listen to it don't rush to the store and waste your money on something that will only make a tiny difference (it's all in your head) of course you'll have bragging rights , so what???? , save that money and invest in something that will put more horses into your new toy, after all ,the sweetest feeling is the victorious one .
just my 2cents