Volvo Forums - Volvo Enthusiasts Forum - Audio Upgrade in Phases, what's the first?

Looking to gain some insight to others "lessons learned" Not exactly thrilled with the stock Bose in my 01 Coupe.

Looking to work in phases for budgetary purposes, as well as utilize available "leftovers" from various other installs.

I would like to keep stock HU for now, due to cost and complexity, as that upgrade would likely be DVD / Navigation System. Although if it is a "must do" first step then a disposal $150 HU can be auctioned.

My current first step is to install rear Sub/Amp for bass. I have a set Polk Subs and 500watt Amp. i also have a decent set of Boston 6.5 2-way components, thinking of dropping in rear factory location.