I successfully upgraded xpenology DSM 5.2 to DSM 6.0.2-8451 Update 2 on my PC with B75MA-P45 (16Gb mem, 3x4Tb HDD).
But .... After the software upgrade, I kept getting an error message via http://find.synology.com/ (no HDD found).
Upgrade with the Synology Assistant, did the trick.