maybe 2.1 is what is being broadcast by the television provider?
i have seen a few HD channels without 5.1 surround sound.
depends on what show.
just last night i was watching something that didnt have surround sound.. then the station went to commercial and the commercial had surround sound.
be sure that the source actually has surround sound, that way you can do a quality check of the problem.
have you gone into the operating system control panel .. then into the audio properties to select 5.1 speaker setup?
5.1 can switch between 5.1 and 2.1
but 2.1 wont automatically switch to 5.1
not unless you program it to specifically do that.