twin loop does sound different, and quite quiet below Vtec. Thats all I know.
But my friend has a Mugen Twin loop and mugen headers on his B18C. It seriously sounds **** to me. When we took off with the car and came back, everyone was laughing at the noise it made. Like some high pitch lancer. It really screams when vtec comes on, but below that, its quiet.
I don't know because it seems there are many who like that high pitched sound.