Your best bet is to go the quiet route. A V-10 is a tough motor to get a good exhaust note out of. If you must mess with it I'd try to mimick a viper system or a SRT-10 system.
I agree with Monkey on the Flowmasters, I have and hate them on my truck. It had a great tone with open headers, than I ran duals w/flowmasters and it created a sound of it's own. BBBBLLLLLLLLLLLAAAAAAAAAAATTTTTTT!!!!!!!