Bc2000 (for the BCF2000 & BCR2000)

Thanks, Martin, you've confirmed what I've suspected before.  It has to do with bit-shifting and such.  Luckily, I've discovered how to access these 'negative' parameters... they're not continuous, but disjunct!!  

In other words, for FX MIX, you do indeed need to use NRPN 65, for all values needed.  It's just that values 0-50 access one half (the 'positive' part, in this case 50/50 to 0/100 dry/wet).  To get to the other, 'negative' values (100/0 to 49/51), you don't logically use the next lowest bits below (and so encroaching into NRPN 64), but instead you use the top end of the last remaining 50 values for the NRPN 65.  In other words:

NRPN 65 0-50 ==> 50/50 to 0/100
NRPN 65 16333-16383 ==> 100/0 to 51/49

Knowing this, it just becomes a matter of assigning these values to an Encoder/Fader using the .tx commands...  I got this insight by noticing that my MIDI-OX uses decimal for the Output Window, but uses hexa for the Input Window.  This lets me see the same info in both formats.  It became apparent in the hexa format what was going on -- what I thought would be a continuous change was instead abrupt, because 06 00 gave way to 06 7F, which is bottom value to sudden top value.  Converting this back to decimal, 16383, then subtracting 50 for the 'other missing half', I successfully assigned an Encoder to transmit the values I couldn't get to before.

I believe now I have to customize an Encoder by inserting a line with .tx commands, somehow involving multiple MIDI commands and the 'ifp' and 'ifn' commands.

If only I could figure out how to customize the BC controls using these scripts and either BCR editor or BC manager...