I do HVAC for a living too. We have installed electric air handlers,
paralleled with gas furnaces. The only way I know to ensure proper air flow
is to put in control dampers in the return, or supply duct, one for each
furnace. I have seen other attempts to parallel two furnaces without
dampers, and they did not work well.
Greg

Why parallel, instead of in series?
Set up the supply air from the wood-furnace to feed the
returns into to other furnace, with a thermostat in
the duct, and set up that thermostat in series with
the house thermostat(s) so that it only goes on
if the air feeding the conventional furnace is
below its designed output temperature.

That way the conventional furnace comes on
whenever the house wants heat, and the wood
furnace isn't providing it. You'll need
a booster fan somewhere, since you're trying
to drive air through two heat exchangers
all the time.