Been chatting this over today, generally to fit a Quad exhaust on the E39 non M5 you have to fit one of those exhausts that run along the back of the diffuser or chop up the spare tyre well to fit a proper setup as per the picture.
But i've just been thinking, what if the below was fitted but with the mufflers removed ? Just do a muffler delete - would mean the spare well wouldn't need as much cut out(if any?) and you could still carry a spare ?
Just run some straight 3" pipes straight through, keep the Y resinator for back pressure etc.