Don’t get offended it means a combination of contradictory or incongruous words.

You say you want to keep your original STi parts, while getting genuine STi upgrade parts. It’s a STi so I’m pretty sure it comes with genuine STi parts. And if you want to keep the parts that came with it then how do you also want to upgrade them? You can figure out what’s already on the car by looking at almost any STi fan club or tuning companies site, try this for starters http://www.usdmsti.com As for how far most have gone to modify, I can say that performance wise most of us have only taken baby steps, like an exhaust/intake upgrade, until the STi ECU gets hacked and broken down so the tuning companies can produce some reliable engine management systems we’re all pretty limited. I don’t think this has been too much help, but I learned what oxymoron means and wanted to put it to use.

 

Here is a good thread to a lot of the things I think you thinking of
https://www.i-club.com/forums/showth...threadid=31387
there are some links at the bottom for ya too.

 

There's a lot of STI parts out there that don't come on the USDM STI. For instance the front strut tower brace, rear lateral links and trailing arms. 52mm STI Genome boost, oil press, EGT gauges. STI brake lines, STI radiator hoses, STI Flywheel, STI Injectors, hell the list goes on and on. The gauges are hard to come by. You have to find someone to go over to Japan and get them for you or find someone who can order them and they are expensive like all other STI parts. Those three gauges alone are more than a thousand $. Just because you have all ATI parts, doesn't mean you're going to have the best parts, but it will mean you have the most expensive. Here's some links:
http://www.vividracing.com/main/ (lateral links, trailing arms)
http://xcceleration.com/itemdetails.cfm85.htm (brake lines)
http://xcceleration.com/itemdetails.cfm86.htm (injectors)