Moonsound Music Editor and Replayer Using only Samples

Nice! Is working quite well already.

So, you're using a VST to play sounds you'll be using in the MSX-version as well? Custom sounds I bet, or did you convert the whole OPL4-WaveROM to Grace as well?

Here's what I'd fear:
- your 5 int example... that's not taking into account int-based tweaks like custom coded pitchbend, vibrato and volume changes. Now make a 24-channel wave tune with lots of Z80-based 'automation' so to say, then check again.
- Are the OPL4's native envelopes and LFOs portable to Grace? Even just a bit off can have drastic setbacks on the end result.
- Grace will make great interpolation and oversampling, resulting in very clean sounds, the OPL4 doesn't (it actually sounds quite tinny). So when playing back at an MSX, the result might be a bit of a bummer.
- Grace will probably allocate a new internal channel to trigger a new note. If you play a new note on the same channel in e.g. MBWave, you'll hear a tick between these notes. Obviously, if you start a silent sample while the previous sound was playing at the max, this gives a tick. Grace has the resources to pick a new channel while the old tone gracefully dies out, I wouldn't expect the same from en OPL4... unless you start cycling through internal channels (e.g. with 16 channels you'd have 8 channels left as a buffer to let old sounds fade away). But doing so obviously means less sound in the end.

Now, these latter two points I usually cope with by acting like an obsessed surgeon, thinking about each step and how to make it sound as good as possible. But that does require you to work with the chip, not with a modern version of the idea of that chip.
Also, do you really require to export, convert and load a tune to check how it sounds on the real thing? That's a rather large feedback-cycle. And I thought the settings scan in MBWave at position 150 was bad already. ^_^

Any of you ever looked into Radium?

You could call it the tracker evolved. Has a (vertical) piano-roll as well.
Not sure if it could fit norakomi's use case, it does have a built-in sampler & extensive scripting possibilities.

The Linux Audio Conference 2014 paper is an interesting read (see 'Info').

There's a nice demo on chance/probability: Radium Tracker - Quick 2Bars Only Demo ( Renoise "maYbe"- Style, Piano Roll inlcuded... ;) ) (Tobias Lutzenkirchen)

That, and Jeskola Buzz of course.. :) (Still wondering how that would've evolved (differently) if it wasn't for the HDD crash..)

I'm not quite sure you've understood my point, or maybe I don't understand your answer, but anyway.
Can you pick a pure/clean sinewave sound, either a short loop or a long 'unrolled' sound.

Then in Cubase, in the key-editor, make this in one bar:
[C5____][C#5___][D5____][D#5___]

This should be the equivalent of an MB-pattern with these notes at rows 1, 5, 9 and 13.
No note-offs, other than a bar just ending when a new note begins.

What do you hear in Grace? If you don't hear ticks at the new notes, then Grace will pick a new internal channel to play while the previous note quickly fades out. If you do hear a tick, then you can indeed simulate the MBwave way of things in Grace. Note that it's not even an MBwave thing, any system with a limited amount of channels would have ticks when the arrangements gets thick enough. The classic Impulse Tracker had a very short fade-out and fade-in at the end and the start of notes, but this is a software effect that probably doesn't work well on an MSX.

* tick = disruption of the audio continuum

Interesting, i was thinking of getting ploque soon to make some opll -ish songs in ableton. from what i read he just converts the midi files to mml. I assume this does not offer too much flexibility from a sound design perspective?