Nice build Steve! For exhaust, I would also the Active Autowerke Gen 3, or one of the UUC exhausts. I love my AA Gen3 on my swap, and our customer's s54 e36 sounds great with that set-up as well!
Shafique's E36: Sorry our CSL "style" airbox takes over after 4k on load...
And the car that initially made our decision on the AA gen 3 + s54 combo easy