Hi Tito - were you able to try Conghoax1's method for the HP Slimline? I'd give it a shot myself, but not quite sure where to start on this (ie, what software you're using to mod).
P9X79 WS bios ver. 3209 P8H77-I bios ver.0904 Already updated to those versions, so cannot use modded older versions. Tried to patch, SLIC certificate appears in AIDA but no activation, got warning that complete slic (2.0)(AMI OEMSLIC) does NOT match, ASUS.BIN matches.