Play layered multiple voices from one midi channel

I'm not talking about splitting, but more about layering.

Hi Pete,
While thinking a little longer about the goal behind your question (as well as the "copy channel" post):

Do to want to mimic the hardware method of changing nature of the sound with the velocity - as instruments have have different sounds depending on the force of playing ?
So if you have 2 or more recorded sounds, they should be mixed differently depending the velocity = force of play.

In that case this info can give an alternative approach, given you have at least recordings of 4 levels.
This is the basis of the grandpiano demo set - I tried with 8, 4 and 2 levels and (subjectively) concluded 4 levels to be enough for this, and 8 should be the ultimate (unless you are a magician on keyboards, but then you can afford more professional stuff than DIY on PI ).

For most instruments, if you have only two they should be mixed as the switch between two will be noticed even by less experienced users.
The good news: I can testify that such mixing gives real nice results on Roland equipment, in other words "it works". They call that layering.
Despite using this technique actively myself I never thought about implementing it on samplerbox...
But it might be that results are even better than the implemented technique and since only 2 layers needed it saves memory and load time.

But I have a hunch doing this software wise is far more complex than doing it hardware wise. So before digging into this: did I catch the background of your question?
Regards, Hans