There's quite a lot out there, but it mainly sounds like you're getting your terminology mixed-up which is why you can't find it.

When speaking of "Soundblaster", people generally understand the Sound Blaster digital audio standard in its various versions, which is not about synthesis.
You're saying you're looking for something to play MIDI in DOS with either FM or EMU synthesis. That's something quite different, even if there were Sound Blasters that could do both, as well as their native digital audio.

I have the feeling this comes closest to what you're looking for, but searching for "DOS FM MIDI player" gives quite a few additional options:
PX Player: play MID and XMI files under DOS

Well the only thing that may not have been clear is perhaps I should have said OPL instead of soundblaster. My mention of Midi was purely to provide an analogy - I'm not looking to play midi files natively on an OPL device.
Ideally I'd be able to download OPL game music and play the audio, without having to load the game. Almost like a SIDplayer on a C64.

JayAlien wrote on 2021-12-10, 22:56:

Well the only thing that may not have been clear is perhaps I should have said OPL instead of soundblaster. My mention of Midi was purely to provide an analogy - I'm not looking to play midi files natively on an OPL device.
Ideally I'd be able to download OPL game music and play the audio, without having to load the game. Almost like a SIDplayer on a C64.

I think what you are looking for is SBVGM. It's a VGM player for DOS. You can download the DOS OPL game music as VGMs from VGMRips. Hope that helps!

JayAlien wrote on 2021-12-10, 22:56:

Well the only thing that may not have been clear is perhaps I should have said OPL instead of soundblaster. My mention of Midi was purely to provide an analogy - I'm not looking to play midi files natively on an OPL device.
Ideally I'd be able to download OPL game music and play the audio, without having to load the game. Almost like a SIDplayer on a C64.

You can Check my player, Mod Master XT, there is a Thread for it in Vogons.
It can play .VGM and various other OPL Based file format.

Thanks for the replies, I'll give the recommended players a try!