To fill out my inquiry, how is the duct pipe connected to the register? Is there some sort of box to which the duct pipe is connected and provides for the supply register to be attached to its' bottom?

Should the supply air vents blow air down the wall or across, i.e. parallel, to the ceiling? There are diverse vent patterns available, for example at the Pex Supply site link provided below.

Here is a link that might be useful: Pex Supply Registers for Ceilings

Here is a link showing an example of how to connect a 6 inch duct to a register. There are variations of these so you can get best fits your application.

I suggest getting a register that you can close. In the summer you may want to close it off so the basement does not get too cold when the AC is running.

Here is a link that might be useful: Register to 6 inch round duct

(Removed duplicate post)

This post was edited by mike_home on Thu, Apr 10, 14 at 8:19