You can only update the firmware associated to the specific model. The Slingbox Pro for the NTSC and PAL systems have certain hardware differences which will brick the box if the incorrect firmware installed. For example, both systems have an incompatible UEI Remote Control Chip which is specific to their own region. Also, the PAL version has a built-in Digital Freeview Tuner where as the NTSC only has a standard analog tuner.
As far as being able to see certain set-top boxes, that depends on the regional origin of the Slingbox as well as the country orientation in the Setup Assistant. If you are unable to see your specific set-top box while going through the Video Source configuration, then Alan Richey maybe able to translate or create a remote update bin file so that you can use your Slingbox Pro with your Dreambox satelite.
I believe he has some prerequisites which are indicated in the following post (https://community.sling.com/thread/3300).