Hi Alain,
Any differences there just look like contrast/brightness/how much autogain is applied (you can vary this in the Sonar Viewer, but not in ReefMaster - yet).
The Sonar Viewer and ReefMaster use completely different methods f displaying the sonar images, it's not really a difference between DirectX or not DirectX. The plan is that the next major version of ReefMaster will include all of the new work from the sonar viewer, amongst a lot of other things.