I don't have the DGA head but I do have the Dichro S head. They look similar, so I assume they are similar (see manual). The condenser chamber is replaced with the diffusing chamber and the lamp house is lowered to the 2-1/4"x 3-1/4" position. It must stay at that position. Use a 50mm lens for 35mm negatives and an 80mm lens for medium format (focal lengths are approximate).
With the lamp house installed, an extension piece is needed to reposition the knob so it clears the lamp house. Not necessary since you don't want to move the lamp house anyway.
As a side note, you may find that your exposure times increase significantly over a condenser head on this particular model. I have come to the conclusion that it is because of the simplistic design of the diffusion chamber. The light enters the chamber and bounces around. Since the top frosted "glass" is the same size as the bottom "glass," it only makes sense to me that if light can get in through the top, it can also get out through the top. This results in less light hitting the paper and thus longer exposure time. Beseler does make an after-market mixing chamber. I haven't tried it, but I do plan to modify my existing mixing chamber.