The only
concern here is that Fluidsynth will consume CPU resources which
the hardware synth won't.
And the hardware synth 'just works', as long as you have sfxload
installed. You could turn a very low spec machine into a flexible
MIDI sound module this way. We've kept our SB Live as a second card
for just this job, even though we have a much better card for
recording audio now.
Try eBay for a SB Live 512 - it shouldn't cost much.
Cheers
Daniel