Anybody have the Volvo Sub-Woofer as an accessory? How does it sound? What's the dealer charging for it? I have got the HU-803 AudioMax sound system in my T5, and I was considering a sub-woofer upgrade. Should I stay with the Volvo part or go with an aftermarket sub. I think the Volvo sub installs under the floor of the trunk and can't be seen. Anyone know for sure? What about an aftermarket sub, can that also be installed under the floor of the trunk? I assume the HU-803 has the appropriate hook-up for a sub already, anyone know? Thanks.