The STI spec Brembo caliper does not use any larger pads unfortunately. The pads Subaru put in the Brembo's on the Liberties were not all that crash hot from the complaints I've read in here - hardly any better than the stock pads in the 2 pot calipers that you have. I have no idea how pads directly from Brembo would perform though.
The stock pads on ours are easily capable of overpowering the tyres at non-go-to-jail road speeds - thus getting yourself better braking power is going to be useless unless you get stickier tyres to make use of it. The only areas where you would be looking to improve the brakes are:
- super high speed fade resistance (and in your area how often are you going to use that?)
- Repeated and extended high temperature fade resistance (see previous point)
- slight improvement in bite
Otherwise, the stockers provide pretty good bite, aren't particularly dusty, are quiet (IMO) and stop well in most temps. They aren't subjected to the poor conditions a dirt bike's brakes are as the wheels will shift most shit away from getting near the discs as long as you are moving.
Fwiw, I have some aftermarket pads in the front of mine (stock in the back) and found initial cold bite a bit less than the stockers. The only areas they have improved on the stock pads has been fade resistance and longevity (80 odd thousand km's on these pads so far and there's still meat left and only tenths of a millimetre wear on the DBA4000's that were fitted at the same time). They may also be a bit less dusty.
Still, I'd be interested to hear what they are like if anyone tries them as sooner or later my front pads are going to need to be replaced