If you do, get the tips cut as close to a standard 3.0 as possible IMO (Or very similar) it looks best!
I don't think you could fit the box of of a sixer, for two reasons, the exhaust is all one piece as standard (up to the cats iirc) and I think the pipe is a different diameter.
If you don't want extra noise, you could actually just have different tips fitted to yours with minimal effort?