Well there are a few choices on the USB front, but if you are just after the MIDI function you can get some basic fangled USB to MIDI i/f. These shouldn't interfere with your sound card at all (it is just a serial type connection and only carries musical data, no sound whatsoever, so you'll need a sound output device anyway). A basic USB to MIDI shouldn't cost more than about $30
I suspect if you go back to the old live you'll notice the sound quality difference, unless perhaps it is one of the higher models (I went from an old ISA Soundblaster Gold to a basic Soundblaster Live and whilst the effects were fun, the sound was naff in comparison).
Might be worth having a look on ebay for something like an emu x2 i/f, sometimes they come bundled with the emulator x2 software.
Hmmmm... Do you have the external I/O connector box. I believe that has MIDI in / out ports. All you should need is a converter cable to go from your 15 pin MIDI cable to the 2 In / Out, 5 pin MIDI cables.
You should be able to pick up one of these on the Internet for $20 USD or less.