Macca,

in short, no there are no inbuilt crossovers in the focus

I'm running a Sony head unit and JBL 5x7 speakers and all is good. Excellent sound quality.

I would think that it'll be something to do with the balance/fade treble/bass setting via your head unit

give it a try fiddling with your settings via your head unit - on some you can adjust rear & front independantly