Theatre 550 WORKING on Win7
My ati Theatre 550 didn't work after upgrading to Windows 7 from Vista.
But it works now.
My system has Theatre 550 pro pci, Theatre 650 pro pci, and Radeon x1650 agp
When starting this, I already had the 9-7 and the 9-10 vista tuner packages installed, but the 550 still didn't work. Remember that for the 550 tuner, it's driver is only in the 9-7 package. The latest one 9-10 does not have drivers for the 550, only the 650
So I downloaded these tuner drivers from ati's download page, select:
windows vista/theatre 550, and download 9-7
windows 7/theathre 750, and download 9-10 (this did not work for my theatre 650, I still required the vista 9-10 package for my 650 tuner)
rebooted my computer, tapping f8 to get the Windows boot options. I selected "disable driver enforcement"
From now on I click no to restart
I ran the windows 7 9-10 installer, which completed with errors.
I ran vista 9-7 installer just to extract the driver files to C:\ati, and cancelled before install started.
Then I went into the device manager
Under "sound, video, and game controllers" I found two entries for "ati unified avstream driver", so I'm looking for the 550. Check the driver version in the properties, the theatre 550 was version 6.14.10.364
I right clicked the 550, and installed the driver manually from the folder C:\ATI\Support\9-7_vista32-64_t550-600-650_wdm\Packages\Drivers\WDM\RIO\LH (note, there is another folder for 64bit)
reboot and everything worked
I'm sorry if this doesn't work for you, but I really don't know what I did to make it work for me, so all I can do is tell you what I did. Good luck.