Hi,
I had a look to the Piano and quickly to the manual. I guess Robert_G is moving the two Part (Lower and Upper) sliders. According to manual, these “Adjusts the volume of…” lower/upper part divided by the Split point. So it makes sense, they send MIDI CC7 (Volume).
As I know some instruments system, I would guess, that Roland FP 60 is using 2 MIDI Channels, once you split the keyboard. So I guess, that the left slider (Part Lower) sends MIDI CC7 on MIDI Channel 1, and the right slider (Part Upper) sends MIDI CC7 on MIDI Channel 2. This would explain, why does it controls Volume.
This instrument is not meant to be for the use case to be used as a master keyboard and send advanced MIDI messages. So it’s not possible to change the MIDI data, which are sent out.
But, if you have Cubase Pro, you can use MIDI Input Transformer to transform incoming MIDI data.
So one of the Input Transformer could look like:
Type Is > Equal > Controller > And
Value 1 (MIDI Controller Number) > Equal > CC7 (Main Volume) > And
Channel (MIDI Controller Channel Equal) > 1
---
Action
Value 1 > Set fixed Value > CC1 (Modulation).
By this you would change, that the 1st slider would be translated to the Modulation.
and the 2nd Input Transformer could look like:
Type Is > Equal > Controller > And
Value 1 (MIDI Controller Number) > Equal > CC7 (Main Volume) > And
Channel (MIDI Controller Channel Equal) > 2
---
Action
Value 1 > Set fixed Value > CC11 (Expression).
By this you would change, that the 1st slider would be translated to the Expression.
Then you can map it freely in your instrument.
I hope this will work for you.