with all due respect, how loud do you need the volume? A X-FI with a (for example), Logitech Z506 500w speaker setup will rattle your windows at 50% volume, and annoy the hell out of others around you
I've been using Creative cards since the mid 90's and the closest thing they ever had was the I/O console which simplified connection to external devices, but these days most soundcards, and even motherboards have optical out connectors.
What about picking up a receiver off ebay or second hand? Is that an option? Pioneer have some cheap receivers. Or some more obsure brands are often cheaper.
But, if you want loud sound, and you want that sound to be quality - not just disortion, trying to do that for under $100 might be a tad optimistic.
I'd be interested to know if you find anything other than an external receiver, that does a good job.
Good luck with the hunt.