You picked up the rasp when you dropped the main cat. (cats slow exhaust velocity tremendously!)
The fact you are running no mufflers and only one resonator also plays a part in not killing the rasp and is 100% of the reason for the obnoxiously loud volume and terrible ricer drone. (though some people think that's "mean" sounding
)
The rear Y has nothing to do with the drone or rasp. It's actually quite well designed. I was surprised at how well it was made (it's a clamshell design) when I cut it apart.
I'd recommend a pair of small magnaflows in the rear location to help with "ricer" noise control. They'll give you a deep tone, but since you still have pre-cats they won't be too boomy.
