I'm using Falcosoft's
Soundfont Midi Player to render my midi files to WAV/MP3 :D It has some menus to let you choose both your MIDI file and your soundfont, don't hesitate to ask it here if you have trouble using it!
I never used Domino but if I understand the situation, the problem is that even though you can listen to your song from Domino, you can't record it to an actual WAV/MP3 file, is it right? In this case, another straightforward approach would be to record your computer audio with for instance
Tenacity or
Audacity while playing your MIDI file in Domino.
A problem with this later solution is that you have to be sure that Domino plays MIDI file in an accurate way and doesn't apply effects that wouldn't be allowed in the MSGS botb format. Well I'm just telling this to be careful and because I don't know Domino well, since it's a tool that's specific to MIDI composing I guess it can play your songs alright ha ha :)