@wolf: The limited amount of instruments of the msx-music did not bothered me much. But it always left me wondering "what if?". Yes Microcabin's music is exceptional, up to a point where they were actually an exception: as in that they are /were clearly levels ahead of what other companies at that time produced, music-wise. For example, as brilliant as that dragon slayer tune is (one that I personally like a lot), you can still recognize the msx-music hardware instruments. What if, msx-audio was a widely accepted standard, what if all msx2/2+/tr that came with internal msx-music had msx-audio instead. My point was: we will never know what music Microcabin COULD have made with msx-audio. Would it be better than msx-music? Worse? the same? (That volume problem you mentioned, I assume, would not have been a problem in this what-if situation ofcourse )
I didnt mean I hate msx-music or its limitations with regards to the hardware instruments. On the contrary, in my mind when I think of msx-music I think of that harpsicord, that vibraphone, that flute. Hardware voices that are so recognizable, almost defining the japanse msx sound of that era. A sound that I, and I think most of you grew up with and have grown to love 
The question is, how much of it is OPL-R-Type, and how much of it is sick musician? 
Maybe OPL-R-Type too asks for overlaying multiple channels?
Below a BASIC demo that does overlay square + triangle.
It sounds like the first 3 seconds of SID Turrican intro.
10 sound 13,14 : sound 8,16 20 sound 9,10 30 sound 0,0 : sound 1,0 40 B = 68 50 a = int(b)*32+8 60 sound 11,b mod 256 70 sound 12,b/256 80 sound 2,a mod 256 90 sound 3,a/256 100 b = b / 1.01 120 if b > 50 then 50 140 for i = 1 to 1000 : next 150 for i = 10 to 0 step - 0.1 160 sound 9,i 170 if (i < 8) then sound 8,0 180 next
Mhm, at the end it sounds like the triangle wave got ADSR!
Without any tracker feature, the PSG is envelope ping on one channel, no ADSR, and "wave" is a word that never has been heard of.
Can OPLL maybe be hacked to pretend to be a bit YM2151? 
That thing is called the OPM and it's available for MSX in the Yamaha SFG-01 and SFG-05 cartridges... And it's completely underused for games (none!).
and it's a pity because OPM was the best chip for MSX at that time. Sharp users know that...
but thanks to mxdrv, we can listen thousands of MDX with our SFG01/05
For its time the Y8950 had very, very good specs (for home computer standards), but was expensive to produce. To use its full potential you had to add extra RAM/ROM which also added up to the price a lot. Keep in mind that 256 kilobytes of RAM sold for around $300 those days. If they really made MSX-Audio standard back then, MSX would have died even sooner because of the price.
Even though the MSX-Music is more limited, let's look at the PC back then with its Adlib and Soundblaster (OPL) cards. Those cards have even better specs, but have you ever heard any good music in commercial PC games made on those chips (FM only)?
With good and smart programming you can get great music even out of the PSG. Many (including me) are lazy or just lack skills and stick to presets without doing any tricks or tweaks 
To be honest, trackers like MB also did not give you much possibilities to experiment a lot. For that you needed something like MuSICA (MSGDRV).
