I have a similar experience; I posted something here about it a week ago. Since then I've used Package Manager to uninstall Flashplayer and then install the latest version from the /extra repository. No difference - video picture is fine but no sound in either Firefox or Opera from video clips (both browsers play WAV and MP3 fine, but using Totem of course).
BTW I have dev-133-x86 for a 32bit PC so your problem is not obviously to do with 64bit AMD. The odd thing is that Flashplayer did work for me when I first installed it with osol-2009-06, and somewhere down the line it's gone.... -- This message posted from opensolaris.org
