I have a yosh-77 on my 08 haybusa and I have the quiet core installed and it is as quiet as the stock system and weighs 36#s less, best of both worlds.
There
are such a thing as quiet aftermarket exhausts. I didn't know Yoshimura made one, but Motad does (OEM-spec - even pass Euro emissions certs) and Hindle makes some as well.
Maybe there's a list of the quietest aftermarket exhausts somewhere? OEM exhausts are
very expensive - if I had to replace an exhaust, OEM likely wouldn't even be a consideration.