UPDATE: The rear discs previously listed are wrong. The correct discs are listed below with the corrected price.
The rear calipers to use are the twin opposed piston Brembos from the 2005-2007 STI Impreza, but they ain't cheap. Checked eBay and the online used parts yards and they're just out of my price range. The OEM Legacy rears are starting to look pretty good. I think I'll clean them, rebuild them, paint them red, load them with EBC Yellow Stuff pads, mount them on drilled & slotted StopTech discs and call it a day.
Then again..................
Obsession is a terrible thing, and I'm obsessed with the idea of bigger rear brakes. The Brembos are too expensive for me so I'm piecing together a kit. Both KNS, Torque Solution, and Kartboy make adapting brackets for the Subaru FHI and Brembo calipers, but the Kartboy is much more expensive. I found the FHI calipers, StopTech drilled & slotted discs, steel braided hoses, and brake pads on RockAutoParts.
DISCLAIMER: This is pure guesswork! Follow this at your own risk. The calipers and brackets will fit each other and the brackets should fit the backing plate. Hoses are hoses so no problem there. It's the discs I'm concerned with. Will they be centered in the calipers and will they align circumference wise?
Brackets (KNS & Torque Solution)
KNS Kit
http://www.knsbrakes.com/c/caliper-items/2282
Instructions: http://www.knsbrakes.com/c/rear-brembo
$199 a set
Torque Solution
SKU: TS-SU-317
https://subimods.com/torque-solution-rear-brake-caliper-adapter-2002-2005-wrx-2002-2008-forester-2000-2009-legacy.html
Similar to the KNS brackets
$199 a set
Calipers (06-07) WRX
A-1 CARDONE 193133 {#26692FE040, 26692FE050} Reman. Includes: Caliper and Hardware
Rear Left; WRX Limited; WRX Model; WRX TR; with Metal Piston
A-1 CARDONE 193132 {#26692FE040} Reman. Includes: Caliper and Hardware
Rear Right; WRX Limited; WRX Model; WRX TR; with Metal Piston
https://www.rockauto.com/en/moreinfo...435927&jsn=770
$110 ea. ($65 refundable core charge)
Discs (05-07) WRX
CENTRIC 12747025L StopTech Sport Drilled/Slotted Disc
Rear Left; WRX Model
CENTRIC 12747025R StopTech Sport Drilled/Slotted Disc
Rear Right; WRX Model
$71 ea.
Pads, WRX
CENTRIC 30904611 StopTech Sport
Rear; WRX Model
$38 ea. x 2
Hoses (00-09) Legacy
CENTRIC 95047505 StopTech Stainless Steel; Sold as a Pair Info
Rear; Stainless Steel Brake Lines
$45 a pair
Approx. Total: $750 (-$130 core deposit = $552)