The fact that the Loudness Sound System converts poorly to General MIDI is only half right.
As it turns out, it's not that the LDS files themselves converts poorly to General MIDI. It's just that the General MIDI implementation of the Loudness Sound System itself sucks.
The MIDI Decoder plugin for Foobar2000 is not only able to load LDS files as if they're actually MIDI files, it's also able to almost properly simulate effects like portamento as it play backs a song, in addition to allowing you to convert them to MIDI files (although it interprets "volume" differently than the midi implementation within Loudness Sound System to the point of being jarring at times).
In fact, out of all the songs in the game, the only one that seems to be the most flawed conversion is "One Mustn't Fall", but that's only because it interprets certain notes of the brass sections as being hold down longer than they should, amongst a few other things.
Here's a link to the MIDI files.
They may need to be tweaked to correct flaws (especially in the case of "One Mustn't Fall") if these were to be used in OpenTyrian. Just a suggestion. Not saying that we should add it.
EDIT: In case you're wondering, I've deleted the link. It was a dead one anyway. I deleted it out of embarrassment. An actual transcription would be more faithful to the original sound material while still keeping in mnd the differences between General MIDI and OPL3. Nonetheless, if you'd still want this, download Foobar2000 and then load the LDS files through there.
It might be that it's not a flawed conversion, but actually a correct conversion - perhaps the notes don't hold out as much when played with the original soundbank (i.e. the note plays that long, but the soundfont has a fading sustain unlike the perfect sustain when playing it in Windows). Personally I've never noticed a difference between OpenTyrian's FM emulation and DOSBox's, and the problematic tracks you mention play perfectly in both.
There's definitely a small improvement over other MIDI files I've seen: portamento parts are properly played.