with an original dmm-image that dreambox can only decrypt dreamcrypt. with an emu installed, you can use cards with other encryption systems. details here.
dre with the original firmware you can drcrypt anything if you have an appropriate CI module (Common Interface for Conditional Access).
I you have a generic one that decrypts virtually everything whereby a single CAS module i.e. Nagravision or Aston or whatever just decrypts the one!
You are talking about softcams! An emu is something different but I got to admit that most available softcams have an emulator embedded!
A little bit reading is compulsory still so i77 please follow dre's suggestion and the link to learn a bit more!
@jpm: i agree with you that with a ci you can decrypt everything. but then it is the ci doing the decryption and no more the dreambox. i thought that i77 was interested in decrypting a card with the internal cardreaders.