multichannel keyboard mapping

I've been working with Pianoteq in Harry Partch's 43-tone tuning.  Obviously I can only fit just over two octaves to play using an  88-key MIDI keyboard.  But the Scala software that Modartt implements enables playing larger scales using different MIDI channels.  I see in the Keyboard Mapping menu of the tuning window that this option can be enabled, but there are no instructions about how to make it work.  The Scala instructions are to put different kbm files in a single folder, each with filenames ending in "_chan", where 'chan' is the MIDIchannel number that plays that map.  Those instructions are intended for playing Scala's synthesizer, but I get no response playing on different channels than the one from the directory that I load into my fxp instrument. 

Can someone guide me on how to do this?

Chris