This could be very simple. as someone else mentioned, there is a lot of panic here without any kind of troubleshooting. Subaru engines are well-built and yes have their known flaws but not unlike every other mfr. many will go to the crusher with perfectly good original engines.
there is no real troubleshooting besides pulling a spark plug at this point.
1. get the codes. this could be as simple as a single position sensor, a bad TPS, a bad MAF, ANY single sensor or wire to it can cause this.
2. I've never been in a tri, but the 'ru's I've worked on were extremely easy if you took the time to look at how it's all settled in there; very few bad wrench points. (I will say, I've never worked on their turbo engines, those look to be pretty tight) for spots on the front of the engine, fans, bottles, tanks all come out very easily leaving gobs of access. you just have to go through it in layers, and the way they mount with minimal bolts but several hooks makes it quick and modular.
get codes. get an idea of why it's running rough. a $5 android app and $15 dongle will do it for cheap....