VirtualMIDISynth fails to load huge SoundFonts

Sometimes after a couple of minutes VirtualMIDISynth just chews up 30% of my CPU for no reason. MIDI rendering speeds up and slows down and artifacts are present in most of the audio. The buffer is set to 450ms, so there shouldn't be any problems there.

Windows Media Player 64-bit is used to play the MIDIs, and enabling or disabling hardware mixing doesn't change anything.

Attempting to change anything in the configuration menu locks the program up and requires Windows to kill it instead of gracefully closing. I think it's linked to the huge SFZ because when I play MIDIs without using that one I haven't seen it lock up. Preloading is disabled because it still doesn't work when preloading the whole thing.