Here's one approach:
http://www.ducatisuite.com/superbikemufflers.html There's always a concern that when you change the stock internals, you'll get more sound but you may end up with less usable power. The stock cans are actually tuned volumes with a specific back pressure, so when you modify the internal configuration you'll change the RPM points at which they resonate. The major manufacturers of aftermarket pipes have already done the dyno work to smooth out or eliminate any resonance effects in their own products. That's why they also include a matching chip to modify the bike's fuel map.
So, when you do it yourself you'll ought to use a UltiMap Eprom or Power Commander some dyno time to get the most performance out of the coring. Alternatively, you can just send them to a coring shop that has done the necessary dyno work, but expect to pay for their development time as part of their labor costs. It's probably best to go with a shop that publishes their dyno charts and supply their own chip.
[Edited on 11-9-2003 by Shazaam!]