Hello all, I'm new to posting, I've been reading up on the forums for a bit now and I couldn't really develop an answer to this on my own based off of what I've read online through searches and watching youtube. The setup I am looking to purchase is:
-Borla UEL Replica Headers
-Magnaflow hi-flow cat - A guy in a forum said his lasted 6 months while only Daily Driving??
-Magnaflow midpipe - Do i actually need the new midpipe to run the setup?
-Borla Hush Catback
I read in another forum that there is an O2 sensor extension required for borla uel's to be installed on a 2.5?
Has anyone had this setup before?
Everything else on it is stock.

 

I have UEL's and when I had a catless mid pipe I had to run an O2 spacer. The spacer did nothing and still threw a CEL.

But it will sound good!

 

I have a cimilar set up on a Legacy Outback; it is the same engine and part fitment as RS.

- I have OBX UEL Headers; had them on for 2 years, no problems. I decided against ceramic coating, but if you have time and can afford the shipping I would recommend it.
- Forget high flow cats, they don't last. Just swap back your stock exaust for smog.
- Yes, get a midpipe resinator, it will be LOUD without it (+5dB?). There is a small resinator built in the UEL and whatever sound dampenning in the muffler, but it is not really not enough by itseld since you will effectively have a straight pipe.
- Borla Hush Catback; are you trying to use a WRX fitment one? I don't remember if there is one for RS or if it has a built in midpipe resinator. If it WRX fitment, hinges will need to rewelded to the right points. I just found it cheaper to go to a reputable muffler shop and have them make me a cat back with a muffler and midpipe resinator (~$100 in labor + $100 in parts). You do not need mandrel bends for NA.
- Yes, you will need to extend the rear O2 sensor as it is located much farther back on the header. I just got spare sensors and made a plug and play extention so I didn't have to cut up the sensor or harness side. Though I still get a CEL from time to time.

Hope this helps!

Edit: I just realized your car is slightly newer than mind, but I think same advice applies.