Further to my post above I have managed to use my HC2 organ to play 3 selected voices from my MOX6 via MIDI, using 3 simultaneous MIDI channels.
That did involve using a free pattern location, and storing the whole mix as a 'master' preset to enable the assignable footswitch to control the rotary speaker speed of both manual voices simultaneously.
The one thing I've never worked out is how to get the expression pedal CC 11 data to control the MOX ?...

Comparing the YC61 MIDI Date implementation chart with the MOX one (see attached copies) and many of the parameters look very similar - so I'm hoping I can connect the HC2 with 3 simultaneous MIDI channels.
But as the YC61 doesn't have 'song' or 'pattern' locations to work from, I'm not sure....

I have had a suggestion from someone looking at the YC61 spec that only a single MIDI channel can be used for this task, but that would be a major retrograde step from the 10 year old MOX 16 channel capability, so I find that hard to believe?.....

I could look for a dealer that offers a 30 day money back guarantee to check it out with the actual hardware, but I'd rather not !

OK -- answering my own query, in case anyone else needs to try out this kind of thing ...
Now I have my YC61 I can confirm that yes, it does only allow reception of one MIDI channel. Or rather 'one' (selectable) or 'All '-- but nothing in between. Youcan't seem to assign several different MIDI channels to different sections simultaneously.
I have found a work around for my own experiment, using the MIDI thru connector on my MOX6. Not perfect, but works well enough for what I was hoping to try out.

Very pleased with the YC61 so far --- currently trying to work out what the 'scale' for rotary speaker acceleration and deceleration means?..
The numbers go from 0.21 to 2.00, but they don't seem to refer to seconds...
In fact the 0.21 setting seems to be for the longest delay setting, not the shortest
And on the rotor setting, the delay so long at 0.21 that I've only ever come across that kind of run up time on a real Leslie when the belt needed replacing!......

I am enjoying playing around though....

Hi,
I come from Germany (here they start at June) and therefore have no YC 61. It will come on Tuesday. But I have a CP73 and the manual is the same at this point. Therefore, I think you can set a midi channel for each master keyboard part, i.e. transmit and address different things on different channels.

From what I read, I think what you say is true for transmitting different simultaneous MIDI channels from the YC61 as a master keyboard, but it can only be set to receive one of the MIDI channels - or all of them at the same time.
I can't find any way of allocating incoming MIDI date to more than one channel....