My Sony 700 has a perfect sound balance with all chips in combination with PSG (Konami/Micro Cabin), but when an FPGA SCC gets inserted, the SCC is way too low... Funny...
Though, I do hardly use the line out of my computer. The soundcards have their own line out, so I have 100% control 
And about the ESC thing. Luckily I never had a 8220 and I popped out the rom from my music module the same day I bought it 
The NMS8250/55/80 had lousy designed audio circuit, a cartridge with 'strong' enough output signal could drown out PSG sound (SCC cartridges being good example IIRC). And a capacitor soldered with polarity the wrong way, or something stupid like that.
Sony HB-F700 has a properly designed sound circuit, but cartridge volume on the low side. That invites you to turn up the volume, which increases noise. Overall not too bad though.
The only MSX I had which had good balanced sound out of the box was my NMS8245
Second that. Ex-owner of this machine, very few issues with sound cartridges, good balance between eg. SCC and PSG. Also the Sanyo Wavy FD2 I had later, was pretty good sound-wise (and internal MSX-Music is never a bad thing 
). Sadly I've never seen a schematic of that machine (let alone downloadable).
MSX-Audio failed because it's cold shit and MSX-Music prevailed because it's hot shit.
I want to again mention combined channels as the hot thing
I think it is what makes most of the show of the vids that Wolf posted.
Try out combinations of instruments.
And, some OPLL instruments can make a nice low rrr. Add it to some instrument and see. Like this
c0 c2
d0 d2
maybe 1 octave apart, maybe even 3, things to try out.
Sometimes want the rrr loud, sometimes maybe just subtle.
@syn,
In moonblaster, press select for msx-music, enter C2, there is the rrr.
Then make a C3 and listen, then make
C2 C3 in two columns
it sounds less like it is an OPL light. More like an OPL full 
You said "is basic music making", while I see it done practicaly nowhere.
"two columns is one voice", things look like this:
C2 C3 D4 D5 D2 D3 E2 E3 F4 F5 F2 F3 G4 G5
The work to be done one time is to find combination of OPLL instruments that make a nice new instrument.
One can do with two times same instrument or with two different instruments. And with 3 instruments. With 1 octave difference or with 2 octaves. Or with 0 difference when it is different instruments. And then one can give each one a different emphasize in volume.
Design of a new waveform. Endless things lurking in there to be tried out, much more than on PSG. And that is not "tricks" like entering register values for every 1/60 second or something.
With moonblaster I got problems understanding what is fixed in OPLL and what is software.
Every instrument got different ADSR, I hope that ADSR is not fixed to that instrument?
In the double-column, both columns are meant to have same ADSR.
