First thanks for anyone trying to help!
Let me clarify what the symptoms are, to avoid confusion.
* System sounds (dings, dongs and startup music) all fine - loud and clear.
* Any media files on the harddrive play fine.
* Embedded media in websites such as flash, .wmv, .asf / .asx - no sound, but the video is great.
* If the website offers the option to play the files on an external player such as WMP it plays fine, with full sound.
Yet when I re-installed Quick Time Alternative, the website media sounds came back, but only until I rebooted.
This is nuts..
EDIT: Re-installed QT Alternative again, and now I have embedded sound again with Youtube, et cetera!
I figure soon as I reboot I'll lose it again.. this is making me crazy.
EDIT UPDATE 2: I rebooted and it was gone, so I re-installed for the 3rd time, this time with IExplorer closed - and after manually deleting the QT & QTAlternative folders - and now Youtube has sound along with all the other sites that would only play video.
I've NO IDEA what the deal was, but I've rebooted the comp 5 times now and fired off every media player I've got just in case somebody was snatching settings - VLC, WMP, WMP Classic, Real Alternative, QT Alternative to see if the issue returned, and so far SO GOOD!!!
Thanks for all the help everyone; I'm not sure what combination of magic tricks worked, but it looks my issue is solved!