I have HKS downpipes and then decat and full 3" veilside system its perfect for me. Much like you I did not want it too loud or boomy, although it still sounds great when being revved not sure if its still available though.
always been a big fan of kakimoto, lovely sound but not too loud. however their was a thread somewhere that said one of the kakimoto exhausts had a restrictor pipe put in it that reduced it to around 2", cant remember which one.
the other option is to go titanium, the best sounding exhaust you can get imo with the added benefit of weight saving. best options are the Tomei Ti, or for a nice sound and massive weight saving, powerhouse amuse Ti, it might be a bit too loud for what you are looking for tho.