Well(as i said) I've only heard a handful of B-series with great sounding exhausts and unfortunately I haven't been in a position to talk to the owners with the exception of one who was at an FPV drive day(the one you get when you buy a GT/Pursuit) and he was a wanker, who would give you that "ahh it's secret" s**t when you asked about the mods he'd done.
I suspect he had a twin 3" diflippo though. Problem is I think twin 3 is too large to maintain bottom end torque unless the engine is well worked.
Soon enough I'll build my own exhaust and let everyone know what it sounds like.

I build exhausts for a living and i have fitted just about evey brand under the sun to BOSS motor to see what works best . On my BA XR8 i run pacemaker 4 into 1 headers, magnaflow hi flow cats and a custom twin 2.5" stainless steel system with 4 magnaflow 6" resonators. after lots of stuffin about thats what has worked for me. the pacemaker and di filippo exhausts dont have a good enough note for me and the manta one does sound mint but unfortunatly the one that sounds best ( with hot dogs up fornt and a round body muffler on the back ) looks a bit rough from the back because you can see the muffler hanging down form rear. just my opinion though. And yes twin 3" and 2.5" into 3" over the rear suspension ie some x force and cobra systems is a terrible idea

Can changing the cats change the note? Getting a manta cat back exhaust on my 3v mont and wasn't sure if i should get cats aswell.

spun body high flow cats do make some difference but i would do headers first/ with the cats, headers make a big diference in note