Unfortunately, I didn't do very much research on it to determine that the T6 is the least favored due to transmission problems. My wife likes the car enough, though, that I think it would be worth rebuilding the transmission when it comes time for it.
Since I do most of the work on my cars myself, I figured I would start a thread for this car listing some of the things I have done and lessons learned along the way (and future lessons). I will continue to update/edit these posts as I go along (and as I find more of the old pictures)
Specs:
2004 Volvo XC90
2.9L Inline 6-Cyl Twin Turbo (B6294T)
4T65 4-speed Transmission
All-Wheel Drive
18x7 Volvo Atlantis Wheels
336mm Front Brake Rotors
Brake Bulbs: 7506
Reverse Bulbs: 7506
Rear Blinker: 7507
Rear 'Position' Light Bulbs: 2825
Taillight Bulbs: 7225
Parts List:
AMSOIL Signature Synthetic 0W-30 Engine Oil
AMSOIL Synthetic Multi-Vehicle ATF
AMSOIL Synthetic Power Steering Fluid
AMSOIL Synthetic DOT4 Brake Fluid
Powerstop Rotors (Drilled/Slotted/Zinc Plated)
Volvo Brake Pads
Volvo Parking Brake Shoes
Volvo All-Weather Floor Mats
Volvo All-Weather Cargo Mat
Volvo Cargo Cover
Volvo Roof Cross-Bars (Thule)
This is the day we picked it up:


First order of business was to change the oil/filter and drain/fill the transmission fluid. Engine oil is AMSOIL Signature Series 0W-30, Volvo oil filter, and AMSOIL Multi-Vehicle ATF. I also drained/flushed/filled the power steering fluid and brake fluid.
The AMSOIL engine oil is said to go 15k miles on turbo applications, I only let it go for 5k before changing it out. I drain/fill the transmission fluid every other oil change (~10k miles).
The tires which came on it were worn Michelin's and we needed to put some on before it would make it through winter. We decided to go with a set of all-season 235/60-18 tires and got a 4-wheel alignment at the same time.
Dealing with the cloudy headlights:
I used a 1000grit and 1500 grit sandpaper (WET) and followed up with Plasti-X polish.



Then, I tinted front windows (20%) and removed all of the emblems from the rear of car; I think it looks much sleeker:

Next order of business was all new brake pads, rotors (drilled, slotted, zinc coated), and parking brake shoes:



Then came OEM floor mats and storage area mat as well as a cargo cover:


































