Summary says it all. Any platform that supports PCI can potentially use a soundcard that requires the loading of SoundFonts. AMD64 is one of them.
AWE cards are ISA. Unless there's some new one I haven't heard about.
My SoundBlaster PCI 512 requires sfxload to load SoundFonts for the MIDI sequencer to be useful. I think all of the other emu10k1 based cards do as well.
Hm. awesfx as it is builts now probably doesn't even work on ALSA, much less x86-64.
I'm using it with ALSA on AMD64 right now. It works fine. (sfxload, anyway). AFAIK, there is no native SoundFont loader for ALSA, but the OSS emulation works.
If you remove snd-seq-oss does it work? (I'd assume not.)
It works fine. snd-seq-oss gets autoloaded when sfxload opens /dev/sequencer, thanks to the defaults in /etc/modprobe.conf.dist
awesfx 0.5.0d comes with asfxload, which loads SoundFonts using ALSA.