How can I connect some other soundfont?

[IlyStra]

How can I connect some other soundfont? Or is that impossible?

[GabrielMiceli]

You'll need to find and install what's called a "softsynth" on your computer to use a different soundfont such as BASSMIDI or fluidsynth.
Once that's installed and configured to use your desired soundfont, you can then go to Midi → Settings → Midi I/O in MidiEditor and then select the softsynth in the "Midi output" column.

[ThreeDeeJay]

I like OmniMIDI too

[PiotrBarcz]

Midi Editor doesn't have it's own built in playback system, it can only output midi to external midi synths.