Your 420 have to be connected like all other legacy DSP.
The 420 have terminals instead of connectors.
Follow the instructions from dpstjp.
Here from Duncan great sides are the Installation procedure
Choices:
a)With 511 as described from dpstjp.
b)No 511: M-5 lead from 568 to master,S-lead from master to "other" slaves.
That "other" slave could be each one, from that "other" DSP on simply daisy chain to all remaining slaves.
c)Custom: You can do a "parallel" or "daisy chain" mix with self build cables or strip/bar. That distribution have to start on the "com out" of the master DSP like the other solutions a) and b)
Audio only:
One coax-cable to each DSP pair
Front,
center/sub,
s�des
rears
The second DSP in each pair is daisy chained from the first DSP in that pair.

Robert


800v3/218/271/8k.2/5k5s smile /5kC/DSP3200/Reviver/
TT-ELP/Graham Slee Revelation/Trinnov Altitude 32/OPPO 205
__Ayon/HB/Shunyata/Miltzow -- power cables,
__Ayon/Jungson/Miltzow --analog, Miltzow-- digital,
__Vortex/WMA ,