is the "chav" shop your talking about motor world?
if so i just happen to work for the bunch of loosers!
JBL stuff is ok for the money you spend on it, but if your after a good set up, you should look at Alpine V power or V12 amps, they do a great mono amp for only about ?150, which you cant really go wrong with,
sub wise i would look at the JL Audio range, i have 2 W0/12 subs which are great little subs,
the W3/10's or 12's are also good sub but a little more expensive,
as for inverting the speaker, DONT!!!! i will sound horrible, you get no deffinition, and not a lot of bass,
as for audiobahn i have always thought the buget stuff to be, well, cr4p, and the top end range way to expensive for the quality of the product,
PPI/Directed also have a gret range out this year, if i were you and had the money i would be buying there stuff!!
hope this is of help,
stu