Reguardless of where you sell it, you will get more money for it by parting it out. You mat not get much for the engine because people just don't trust other people when they make claims on engine life. If it were new, that would be another story. Used=bad. The XS3 should fetch a lot by itself even being used. The kit looks really new so you should be able to sell it for as much as %75 of what you paid new.

If you sell it as apackage, you'll get like 50% of what you put into it.

If you part it out, you looking at maybe 70%, plus you can make a buck or two on shipping like previously mentioned.

The sad fact is that people just don't have money to buy it as a whole and pay what it's worth ($700-$800). $180 for a slightly used XS3 is very appealing though. Then another guy is like "damn, $300 for a barely used MBX4". Yet you might not be able to get $480 out of it total and we didn't even go over the engine and pipe yet.

Part it out. More money.

Good Luck.
-RobH