Sphere doesn support MIDI files anymore! How do I use them?
When Sphere’s sound engine was switched from FMOD to Audiere, Sphere lost the ability to play MIDI files. You can view the rationale here. To play your MIDI files in Sphere, you’ll have to convert them to Ogg Vorbis or MOD files first. You can use Timidity++ to convert to Ogg Vorbis, and gmid2mod to convert to MOD (XM, actually). Search on google for downloads and more information. You may also use a program called WinGroove to convert from MIDI files to WAV files.