Yamaha MU90R Owner's Manual page 72

The Part Mode settings differ depending on the Sound Module mode
selected, as described below.
For XG (Extended General MIDI) mode:
All settings described above are available. When normal is selected,
any of the basic or the extended set of Voices can be used for the Part.
For TG300B mode:
The settings normal and drumS1 — S4 are available; drum cannot be
selected. When normal is selected, either the basic or the extended set
of Voices (for the TG300B mode) can be used for the Part.
For C/M mode:
The Part Mode settings are fixed in this mode and cannot be changed:
Parts 10 and 26 are set to drumS1, and all other Parts are set to nor-
mal. The MIDI Receive Channel setting for Parts 1 and 17 is set to off.
The 128 Voices of C/M Type 1 can be used for Parts 1 — 9 and 17 —
25; the 64 Voices of C/M Type 2 can be used for Parts 11 — 16 and 27
— 32.
For PFM (Performance) mode:
All four Parts are set to normal; none of the drum settings are avail-
able. Any of the basic or the extended set of Voices can be used for
each Part.
NOTE
When two or more different Parts are set to the same editable drum setup (drumS1 — S4),
any edits made to that drum setup automatically affect all those Parts. For example, when
two Parts are set to drumS1, any changes made to drumS1 affect both Parts.
Mono/Poly Mode
Height of bars indicates selected Mono/Poly Mode setting for each Part.
(A single bar indicates "mono" setting, while full height indicates "poly.")
Selected Part and MIDI channel
MULTI MODE
6 3