its the amalgam of different parts on there. I'm currently in the process of selling off my UEL setup and it sounded amazing (borla headers, stromung hfc, stromung type xa catback) and now that im temporarily running around on EL headers I hate the sound, honestly don't know how anyone can bear this noise coming out of a subie when they can have boxer rumble, I actually refuse to go anywhere in the car except for the final drive to the shop on monday when the boosted build begins.
The truly sexy blurble you seek is easily attainable, you just have to do it right, the straight through cat pipe may be part of the issue, cuz that makes it sound like crap, and there might also be somethin in that muffler, AND the ebay headers may have a leak or the different parts may not line up and seal properly thus causing a leak there, or it could be a combination of things. The truth is (all do respect) I think its the different parts working against you and if you want the truly sexy blurble, stromung or bust (i've seen the ebay headers work well on a car but that car had a stromung exhaust on it lol (the boxer4racing 2.5rs autocross car)). Hope you find a remedy to your issue, though I'm not sure if switching from the jumble of parts you have now to EL is the way to go (HATE EL!!!! Sorry I'm biased, but for a darned good reason)