More Ways To Get More Horsepower?
I've got a 1996 Mercedes E320 with: Magnaflow Performance Catalytic Converter, a 3'' Exhaust System with Magnaflow Turbo Muffler, K&N Air Filter + Cold Air Intake, Performance ECU Chip (the REAL deal from AMG), AMG Turbocharger, Small Electric Forced-Induction System and a 20 lb. Wet Shot Nitrous System.

Any ideas for more ways to get a little more power out of the engine? I am planning on racing this car, and money is not an issue. The upgrades do not have to be street legal, either.

port the engine, upgrade cams, ignition, fuel system.
(just a few ideas)

Cam, headers, ported heads, larger injectors and throttle body, balance and blueprint engine, sodium valves, roller rockers and lifters..the basic hi-po stuff.

have you thought of different heads ported and cams or maybe direct port nitrous induction maybe a bigger turbo or a smaller cam how about a boring out the block thats in it now bigger injecters a more gpm fuel pump bigger throtle body and how about some roller rockers and weight reduction

Since money is not an issue, l strongly suggest you change the whole engine to an AMG E55 twin aspirated engine with 588BHP. It is by far the biggest horse power ever produced for E class. You do not even have to mess around with the internal parts cause it comes complete, you may need to change and or reprogram the engine control module. But then again why not purchase the latest E55 !

Since u r racing, l do not know when all of the upgrades where made, but l would double check the transmission to make sure it can handle all of that torque, it may very well need to be reinforced, check the gearing to better optimize the power to the ground as well as shocks & springs, so that the car is dialed into the track. Take a look at body reinforcements or braces & most importantly, figure out which brand/size of tires makes the most sense with ur set up. You may have this sorted out, but l did not see it on ur list of upgrades. These adjustments will translate the power u do have into torque, which wins races.

Since your car is already modd-ed out, the room for additional performance is getting tighter.

Every machine reaches a limit on what can be done with it.
l am surprised your engine has not blown up yet.