In terms of getting more noise out of it without compromising plan, the valve controller is your best bet.
BMW haven't released an M performance exhaust for the M60i yet and even if they did it wouldn't be worth it at their premium.
Unrelated to your query, but the M60i is probably the best value for money daily performance SUV on the market right now. Its more or less 90% of the car the M Comp variant is, but way more daily friendly. Its a proper sleeper.
Please do share some pics of this beast if you can.