new paradigm 6+3=9 bits: three S&D drives, 8 axes... , 3 bits spare

In my upcoming professional CNC router kit, I am
facing the problem of lots of auxiliary axes:
multiple Z heads, dual/triple/quad Y axes,
dual gantries, table raising/lowering etc etc.

This severely constrains using the parallel port
with its limit of 12 output bits (6 axes max),
and one would desire to reserve some for
spindle ON/OFF, vacuum ON/OFF etc.

The new idea is to use and power only 3 drivers,
each of which can be electronically 'hooked up'
to any of 8 axes (lets assume bipolar only).

In almost all cases, only 3 axes or fewer will
be moving simultaneously. If you need to
reposition an A,B or C axis, then assign
driver #1 to A momentarily and change A,
then switch back to #1 driving X.

As there are S&D 3 drivers hooked up, thats
2*3 = 6 bits. Using 3 bits for 'assigning axes'
that gives a choice of 2**3 = 8 axes. 6+3=9,
so that leaves 3 output bits spare (for Spindle,
vacuum, etc).

Lets assume for the sake of argumentation, that
if the 3bit assignment bits change, then
the next (of the 3 available) "D"'s to flip
get assigned to that driver now indicated by the
new bit pattern. Flipping D's should not affect
positioning adversely.

- - -

This circuit could also be useful to those
guys who have a mill AND a lathe, but only
want to buy 3 drivers. With everything hooked
up, a software macro is called to activate
either the lathe's motors or the mill's motors.

Any comments from the electronics experts about
the ease (difficulty) of creating this
triple (4 wire for bipolar) 3*8 cross-switch?

Doug Fortune
http://www.cncKITS.com