Windows 7 HDMI connection has no sound

I need some help getting the right driver loaded and enabled for sound on an HDMI display.  Long story, but I had problems extending the display from an HP EliteBook 8440P using the integrated VGA port in both the laptop and the HP USB 2.0 dock.  Video would run for a while, then blink out and default back to no second display selected.  No great explanation for this other than I suspect problems I can't fix in the driver and or graphics.  No driver choice for this, that I tried, improved the result.  Also tried the options from the HP support site, including the drivers for the USB dock that included DisplayPort video.  The display I'm extending to also has HDMI.  The HP USB2.0 dock has DisplayPort, so I did a passive cable conversion to the display HDMI port and find the video to work as expected.  The audio, however, does not.  In the image of W7 Pro-64 on the laptop, I have no HD Audio device listed in Control Panel/Sound, or Device Manager/Sound, video and game controllers.  I did a clean W7 Pro-64 install on an identical laptop and find a sound device in Control Panel called Digital Audio (HDMI) using a Microsoft High Definition Audio Device, version 6.1.7601.17514 signed by Microsoft.  So far, no combination that I have tried of Windows Update, scan for changes or show disabled or disconnected sound devices on the original laptop gets me any closer.  Web searches related to downloading that driver haven't got me there either.  I don't know how to copy a driver from one laptop to another.  Ideas?

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Lee W, MVPTechnology and Business Process AdvisorCommented:
Keep in mind that while sound usually works over HDMI, it doesn't HAVE to.  Some implementations don't support video and sound on laptops/graphics cards.  I don't know if that's the case here, but keep in mind, you could be trying to get something working that won't.  Period.
HerrBallAuthor Commented:
As a supplement, I expected the HD Audio driver to work on the second laptop, but had not tested it.  Turns out that device in Contol Panel/Sounds is enabled, driver working, but it's not eligible to select for use.
HerrBallAuthor Commented:
Additional information...  The HDMI device I'm trying to use as a second display is a Mimio projector.  I duplicated the situation and connected it to my Panasonic TV.  It loaded a Panasonic driver and everything worked as expected.  Going back to Mimio with my questions next.
HerrBallAuthor Commented:
Problem solved - in this case, a USB cable was required to load drivers from the projector (as explained by Mimeo tech support).  Turns out using a USB 2.0 cable with active 2.0 extender had been problematic before.  They recommended using an extender that converted to UTP in between and presumably handles their USB 1.1 port better.  I had to ask the question 3 times, 3 ways to get this answer....

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HerrBallAuthor Commented:
Expert answer was appreciated, but only presented the possibility that this just wasn't going to work...
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Windows 7

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