First of all, is your box Original or Clone (Sim 2.30) ?

If your box has a chip (so no Sim), it should be an original box, and you can use the OpenATV images for DM520HD/DM525HD.

OpenATV for DM520HD/DM525HD
http://images.mynonpublic.com/openatv/nightly/index.php?open=dm520

Or you can use PurE2 for DM520HD/DM525HD,
http://www.ourdreambox.com/ubbthreads.php?ubb=postlist&Board=184&page=1

TS
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DM8000, DM800se, DM500HD, DM800HD, DM7025, DM7020s, DM7000, DM500s
VU+ Solo, VU+ Uno, VU+ Duo, Kathrein UFS910
Tivusat, TNTSat, Fransat, SSR/TSR, BBC1-2-3/ITV
DE-OpenBlackHole 1.4 image : http://www.openblackhole.com/