First of all welcome!
I would check out one of two places.
The Sound Choice (
Pacific Northwest #1 Experts in Car Audio/DVD applications, "The Sound Choice".) - they do some high quality work, and I have never really seen a car done bad by them.
or
503 Motoring (
503 Motoring) - You will probably pay more at 503 Motoring because they have became extremely popular in the area doing a lot of the Portland Trail Blazers cars. But still do high quality work.
Hopefully that helps! Good to see another X5 owner in Portland. Hopefully I will see you driving your X around somewhere!