Thanks for the response.  You are right, apple uses them as M4A files, but .AAC is actually ISO standardized version of MPEG-4 that Apple and others adopted. (See Wikipedia cite below.)  Apple calls them .M4A files, but they are the same as .AAC.  Media Monkey, Windows Media Player, Etc.can all...

Hope someone here can help me.  My new HM-801 (.19 Firmware) will not play AAC files.  FLAC, OGG, WMA, MP3 all work.  Just locks up when I hit play on a AAC: Onboard or SD.  Specs say it supports AAC; does it really?  Any help much appreciated.