well first of all why not flash to the latest R8 version of the w580 firmware?
look here for a generic Main and a FS and corresponds to the languages in your phone and use the same customization as your FS.
Second, just flashing to a generic FW wont unclock your phone, you need to patch it with the Sp-Lock patch.
here is the code for the sp-unlock patch for R8 w580:
;W580 SW-R8BA024
;Remove SIM-Lock
;(c) IronMaster
;(p) simox SIM_lock_remover patch generator v2.0
+44140000
4F1DC4: 30B5041C00231A1C111C1C208CF4 F0B505213A2293F495FB0020F0BD