on my TT for a while and couldn't handle the drone of them between 2k and 2,800k so replaced with Specialty Z cat back. Much better sound and no drone and will fit with the HICAS.
Or if you still decide you want the MagnaFlows and you you can't return the HICAS elimination bar you bought you could try re-selling it here in Classifieds or on Ebay and then buying the correct bar for your year of car.