The ECU will take a while to adjust to the increased air intake. I'd give it a week or so.
I've never heard that Jabba one before, but am surprised about your findings.
My BMC one sounds nice & throaty, with a louder 'chatter' when you lift off (but not longer in duration). My mate said it made my car sound like a 330 when I was downchanging on the way to pick him up from BMW!
Jury's out with any extra power/throttle response, though. (I defy anyone to notice an extra 2-3 bhp!).