Why do you have a BOV on your stock turbo? The recirc, especially in your year (being older they're still made of metal ?) are perfectly fine up to 19-20psi. Am I wrong?
Don't get me wrong, I love the tsst as much as the next guy but it just seems pre mature for the car on the mod steps.
As vision said, turbosmart. Their 50/50 valve is getting great reviews all the way across the board and may be the best option for you at this stage in power.
*not a Subaru or BOV expert by any means, just read reviews and personal experiences.