I know on the WRX/STI exhaust I would have to modify the front flange to fit it to the RS.

My question is can I use a Stromung midpipe with an STI axle back or is modification still needed at the last flange?

If this is for your 01 RS, then you have to rotate the flange a bit on the STI axleback to meet up with the stromung mid and relocate the hanger to meet the RS's. Expect to spend from $35 to $65 for a local muffler shop to do the job for you, much better if you can do it yourself. Good luck....

Thanks... exactly what I was look for :D