I have been running a similar setup for a little over 1 month now - STi TMIC w/ WRX scoop/splitter. I removed the rubber shroud from my WRX splitter, and built-up my own with vinyl & foam weatherstripping (yea, it's redneck, I know). The foam weatherstripping is not holding up as well as I had hoped, but I still think it is better than nothing, or the smaller WRX shroud.
When I was cruising at ~70 a week ago my EGT's suddenly shot up, and would not come down, I had to slow down to like 40. They seemed to be very erratic, and at first I thought my EGT probe/gauge must be going out. Luckily I was almost home, but somethind definately was not right. My temps almost never get above 1450, and I was at 1600. It seems to be doing fine since then, but it still has me worried. This was at night when it was about 70 degrees, so it may not be the splitter/shroud. It may just be that I am still running the Cobb stg 2.5 map, I remembered seeing somewhere that Cobb recommended keeping an eye on EGTs if you ran that map with the STI TMIC.
I looked at Rallispec's site yesterday and could not find the splitter, did you just order one? I sent them an email, but have not heard back yet. It looks like they just re-did their site though so I am hoping they just have not finished that part. Let me know how everything lines up with yours, I am curious how well it will seal since I think it is designed for the larger JDM STi TMIC. It has to be better than what I have now though.
How much boost do you get now that you got it tuned? I still need to do that too, but I don't know of any good shops in the Denver area that have Protuner. I may just take a road trip to Salt Lake City.