Vector control is only possible if you have 32 or 64 parts active.

In vector mode parts will still play together but the vector controls can change their volume, pan, filter cutoff in pairs, controlled by user defined CCs set up with NRPNs

You must set the X axis CC before Y, but if you don't set Y at all you can run just a single axis. If yuo only have 32 parts active Y settings are ignored.

e.g.
Parts 1 and 17 can be set as x1 & x2 (volume only) while parts 33 and 49 can be y1 & y2 (pan only)

Independently of this Parts 2 & 18 could use filter and pan from another CC

Setting up is currently done as follows.

In the required channel send:
NRPN MSB (99)  set to 64
NRPN LSB (98)  1
Data MSB ( 6) set mode
              0 = X CC
              1 = Y CC
              2 = X features
              3 = Y features
              4 = x1 instrument (optional)
              5 = x2 instrument (optional)
              6 = y1 instrument (optional)
              7 = y2 instrument (optional)
Setting CC for X enables vector control any value oustide the above list disables it.

Data LSB (38) value to set

features:
    1 = Volume
    2 = Pan
    4 = Filter Cutoff (Brightness)

 
An Example:

From channel 1, send the following CCs

CC      Value
99       64
98        1
 6        0
38       14
 6        1
38       15
 6        2
38        1
 6        3
38        2

This will set up CC14 as the X axis incoming controller and CC15 as Y, with X set to volume control and Y set to pan control.

You can either go on with the NRPNs to set the instruments (this will load and
enable instruments from the current bank) or enable and load them by hand.
For channel 1 this would be part 1 and 17 for X and part 33 and 49 for Y
