Homers, you are right, no sound when using the HDMI output.
I think dream fixed the HDMI issue in the latest firmware, according the the changelog of v2.8.0:
Code
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miscellaneous
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fixed dm500hd bootproblems with some powered TVs during bootup
Would be nice if someone of Dream or the moderator could mention this in this thread!
Now I wonder if the sound issue will/can be solved with a firmware update.