exhaust manifolds

to do manifolds is an engine out job. rs6 manifolds connect to the turbo then to downpipe.... check some aftermarket suppliers for more exhaust stuff , but supercharger is your best bet for ok power increase on a 4.2

having said that lower the compression of the 4.2 and bolt on those rs6 turbs you might see more like 600bhp than 480bhp of the supercharger

wouldn't have thought either was an easy option, both would require significant engine modifcation (internals), Intercooler, fuelling upgrades and either custom or alternate exhaust manifolds.

What supercharger? Eaton?
on an 03 car, I would have though the cost and the massive depriciation you will see on your car if you came to sell it would make it worth your while getting a late b5 rs4, you could even pick one up with MTM st2 or 3 upgrades.

either that or get your V8 on DTH individual throttle bodies with standalone ecu and a proper remap, should see more like 400bhp then, it would be easier to remove your upgrades if you sold it

just my 2p