I just finish my brembo conversaion. Any brembo's from 04 to 07 will work on the legacy gt. The rotors have to be 5*100 from the 04 STI. The front will bolt up perfect with the 5*100 rotor and 04 to 07 sti brembo caliper.
For the rear i used some oversized brake shoe from the UK for the rear STI stock rotors because the Legacy GT brake shoe will not reach. U also need a pair of bracket fot the rear brembo's to bolt up. U have 2 sets of bracket. (1) u have to grind away a little space for them to fit. (2) the brackets that bolts up without any modifications. The difference is price.
The UK has brackets and brake shoe for 1 somn. Yimi sport $195 and fastwrx $249 for the brackets only. I had to change my rims after Tho.