Some good advice already. As far as the system goes, I'd agree with Warren: start with the source. I don't think you need to drop the entire $1500 there. As he suggests, you will find that upgrading a single component may lead to revealing faults elsewhere. I would think you can find some source bliss in the $1k range that would still be a significant improvement on your Cambridgge and put aside the balance for the next upgrade. Also, as has been suggested, FIRST look at the room as the source of your problems. A room can make or break even the best of systems, no doubt about it!
Marco
Marco