10HD is the only channel in Canberra broadcasting 5.1 channel AC3 sound. It's possible that this is causing your sound issues on playback.
Unfortunately it looks like the Beyonwiz forum has died, but I seem to recall some posts about AC3 downmix, and Google (limited in what it shows of the forum posts) has "AC3 downmix is on by default" and "If downmixing is enabled then all channels are treated the same".
I'd take a look at that, and if downmixing is off (or disabled), then try on (or enabled).
Unfortunately it looks like the Beyonwiz forum has died, but I seem to recall some posts about AC3 downmix, and Google (limited in what it shows of the forum posts) has "AC3 downmix is on by default" and "If downmixing is enabled then all channels are treated the same".
I'd take a look at that, and if downmixing is off (or disabled), then try on (or enabled).