It probably isn't worth the trouble messing with stock cans. Save up and get yourself a full system. I was shocked to find that it will cut over 20 pounds off the Busa. Stock is cast iron (not really) but it weighs 35 pounds with cans. My Akrapovic full system with a titanium can weights 13.5 pounds and sounds great. Slip-ons will only save a couple of pounds because you have to buy two cans for stock replacement and all of the weight is in the stock header pipes. And they cost almost as much as a full system with single can. I got mine for $820 for a Akrapovic race system - Thin wall stainless header into titanium can. Full titanium pipes will save a pound or two more but cost half again more.
Stock pipes are small diameter and sound relatively high pitched. The Akrapovic pipes are larger in diameter to flow and sound lower in pitch. Great rumble at idle and literally bark when rev'ed. Most of the quality aftermarket pipes have the same weight benefit if they are racing types. The sound will vary slightly.
Let us know what you choose to do, especially if you mod the stock cans.
If all you are looking for is sound, get yourself a couple of drill bits 12" long, 1/4" and 1/2". Take off the canisters, remove the polished stainless cap (you will have to dremmel the welded areas on the heads). There are two steel plates within the canister one in the middle and one at the end. Start with the 1/4" and drill pilot holes in the center plate. (I drilled 9, 1/2" holes in the center plate) Be careful to get the holes centered evenly because you will then be using the 1/2" for your final. Then drill out the end of the pipe. Replace the endcaps, use a little high temp lock tite on the screws, and replace the canisters. You will definitely get more sound, mine was louder than my BDE Gen III.