RSF fireplace central heating connection question

[tradertedd]

I am scheduled to have an RSF woodburning fireplace installed in about a month or so. I see they offer an option for connecting this unit to the existing central heat ductwork in my home and that this connection occurs at the air handler plunum. My question is can I make this connection at the return air compartment instead, thereby utilizing the blower in the return air compartment to draw warm air from the fireplace and distribute it through the ducts, rather than have the optional fan pushing the warm air into the plenum.

Also, I have a hydro air heating system in my home that uses a boiler and two air handlers, one in the basement for the 1st floor, and on in the attic for the second floor. Does anyone know if it is possible to connect both of these air handlers to the fireplace?

Thanks everyone