You can only have either DPF or HAM, not both. With DPF you can have 2 playfields with 8 colors (ECS) or 16 colors (AGA) each. HAM needs all 6 or 8 bitplanes, there is no room for a second playfield.
One could hack Workbench into HAM mode, but it's not yet possible to have a proper looking background then. A new picture.datatype would have to be written which recognises a HAM screen as destination.
