Well I got my subwoofer working last night
It's temporarily in the passenger footwell
I'm not sure whether I even need my rear speakers now at all - they are cheap rubbish at the moment and the bass sounds disconnected and delayed compared to the rest of the music. Whereas the subwoofer sounds tight and in time with the rest of the music, which is a bonus!
I was thinking of maybe getting rid of the 6x9s in the
back parcel shelf, and maybe putting in some more of these JBL 6x4s, and then they'd match the front speakers both physically and sonically, and just rely on the sub for the bass. (plus the 6x4s could go in the original manufacturers speaker holes)
The rear parcel shelf is a replacement made out of hard plywood that's nearly an inch thick!!