Hi, yes I have gone for the JBL system which is by no means Audiphile quality but in my opinion is certainly a better overal sound than the standard system. the treble is reasonable and the bass very good. Having previously used a sub in my previous vehicle it is not really necassary with the JBL unless of course you want to go for a ground shaking experience.
My observations are that the sound quality from CD's and well recorded ipod files are far better than that of the radio which is to be expected. The purchase of a digital radio tuner maybe an option to get over that one. It coud be be plugged directly into the jack socket. Just a thought.
The unit does look as if it can come out independantly as it does have the usual 4 holes for the removal tools in which case you should be able use an output for a sub, even if there is not a specific sub output.
Hope that helps.
