I've got a 622 VIP and I lost my audio over the HDMI port as well.... my video went about a week later. May be unrelated, but Dish seems to have a lot of problems with HDMI on their equipment:
1) Their hardware runs quite hot and isn't ventilated very well. Often leads to premature failures.
2) Whatever company they subcontracted for their hardware (JVC in my case I believe) used a sub-par HDMI port connector that's been reportedly known to break quite easily when stressed even lightly - i.e. just plugging the HDMI cable in.
3) Reporting a failed HDMI port to their phone tech support staff/agents will get you the canned response that there is a "software" problem with HDMI ports on Dish equipment (particularly the 622, not sure about the 211) that is supposedly going to be fixed via a software update sometime "soon"... closest date I could get them narrowed to was October/November time frame.
In your case, since you only lost audio, I'd unplug the unit and let it sit for an hour or two. (Just in case it is heat related) Then plug it in and let it boot up. See if that clears the problem. If not, you may be in the first throws of HDMI failure like I experienced. If it does clear up the problem, odds are its heat and you may want to look into improving air flow to it.
Good luck!
--Johnno