OK then, noted that you want an emulation of the 10V analogue control
voltages.  This should be quite easy as you generally don't need very
fast changes (faster than say, 100 ms).

  PWM or duty-cycle modulation is definitely the way to go.  Take the
output from the PIC for each channel, filter it by a simple R-C filter
(perhaps two-pole) with a calculated cutoff of about 20 Hz, then apply
this to an op-amp driving a PNP power transistor (Darlington perhaps)
supplied at 12V. The op-amp multiplies the 0-5V signal generated by the
PIC by 2 using a 2:1 feedback divider.

  You'll have to scale the power transistors according to the load
provided by the dimmer bank (each channel).  Presumably the input
impedance is purely resistive and returns to ground, so can be checked
with a standard multimeter on a resistance scale and confirmed by
hooking up a variable supply and measuring the current drawn at 10V.

  If you have many channels, or you want to "remote" all this from the
PIC, you may wish to use latched shift registers as output expansion
from the PIC.  Mmm, maybe that's another story!
--
  Cheers,
        Paul B.