upgrade exhaust

What's good 7 series fam????......I drive an 03 745li and I wanna upgrade the exhaust but I can't run dual mufflers on both sides but the car has stock dual mufflers running from one exhaust pipe so can I upgrade the stock mufflers if yes do I need to go with 2 or can I replace with one

1) You actually can run it on both sides - see pelonx1st's setup.
2) You can do either - replace both mufflers with one or just replace the smaller muffler with a straight pipe or a MagnaPack. Look through my threads for the one about an exhaust and you'll learn plenty