somewhat apropos of this, I just got an akra slip on from IND and paired it with a fabspeed center (x and hfcs). Great customer service and price from IND. The exhaust is, I think, what I've been looking for. It is a bit loud and boomy on cold start, but once the car settles into idle not obnoxious. Deeper than I would have thought it would be (much more so than just the fabspeed, which was on the car first for several thousand miles).
Very little intrusion into the cabin under steady cruising. None of the boom or drone of, say, an eisenman race at lower rpm. I thought the Akra might make it higher pitched (people say F1 like), but it still sounds pretty deep and muscular to me. Under acceleration, it just sounds magnificent - great with windows closed, all I could want with windows open. Not so loud as to get me in trouble with the neighbors or my wife - haven't tested it on my kids yet.
anyway, for those of you cautious about adding a lot of volume, a great combo. and akra quality is as described.