I didn't think much of the Volvo calipers actually. In race situations they didn't do much better, if at all, than the stock TR8 calipers. The big thing is heat, not clamping force, and going to a vented disc is the biggest improvement you can make (illegal for me, I have run two ducts to each side).
I also ordered a "TR8" master cylinder and brake booster one time from one of the reputable British parts houses. It ended up being an SD1 master cylinder and booster -- slightly longer master cylinder and the booster felt more boosted.
In any event, I don't think the TR8 master is the weak point in the system. It's the solid rotors and small pads. Go with vented discs if you can, and then bigger calipers (the 240s were nearly identical to the TR8 calipers).
Last, get the rears to actually work. Modify the prop valve and put some good shoe material on there. That will help tremendously in getting front brake temps down and overall brake performance increased.