I think you can if you put them in a resource pack and then refer to them in the config file, but I'm not sure, I use the default XP sound (and I love it).
It is definitely possible, but no one wants to do it because it raises a lot of moral/legal/etc issues.So yes, it can be done, but no, it will not be done. Ever.
Ding! is awesome, I've been using it for a while now :)