The main hardware limitation is, >ST chipset model STi7101 (ST40 with SH4 Core)
As I understand it, Enigma 2 Images were created and compiled for the Dreambox HD family, using Broadcom CPU's.
The drivers for non-broadcom CPU's do not fully support Enigma 2, which is why these Images do not run as they should on ST based receivers.
These ST based receivers run a modified version of Enigma 2.
You may also have noticed, CCcam (standard in DM's) is not supported and other emu's, ie; mgcamd has to be modified, as well as countless OScams.
Other set top box manufacturers have incorporated the broadcom chip, ie; VU family and readily run all aspects of Enigma 2 Images, including all emu's as used by DM's.