I beg to differ...throw on an Apexi N1 or Cheapo muffler and I guarantee it'll sound ricey..With a BMW 3.0L I-6 you'll NEVER have to worry about sounding like a p.o.s. honda.
As far as intake roar...yes, no matter what you do, doing an aftermarket intake will make your intake louder. The engineers design the stock intake to flow somewhat efficiently but be quiet...which is why you have that huge airbox.
Now..as far as a quieter intake...the true cold air systems that keep the filter out of the bay will seem quieter in the car than an underhood...They are farther away from you and won't resonate as well as the filter would if you have it in under the hood.
You really can't get a "quiet" performance intake...other than changing out your stock airfilter for a K&N...but that is essentially worthless.