How far can my lead wire run from the CPU to start of VENTRIX channels?

There is no guideline specifically for the feed wire from the CPU to VENTRIX channel, however there is one for the total feed + channel length.

Max Feed + Channel combined length (12AWG power & 16 AWG data wires):
96W, 150W, 320W: 200'
600W: 100'

Please see the chart below for visual reference: