The Denon AVR-591 does not support user-accessible firmware updates, as it lacks network or USB ports for such procedures. There is no official "patched" firmware, as updates require specialized service center equipment. For issues, a factory reset is recommended, which can be performed by holding the surround mode buttons while turning on the unit. More information is available in the Denon AVR-591 Owner's Manual DENON AVR-1611, AVR-1621, AVR-591 Service Manual