Pioneer VSX-520 and ATI HDMI issues

Thanks for any helps on this one, its got me tearing my hair out.

I've got a HTPC with a new ATI 5450HD with HDMI, connected directly to my Pioneer VSX-520

The LG 42LC7D LCD-TV is connected to the HDMI out on the VSX-520.

Here's what happens in a nutshell.

With no catalyst drivers installed, standard Windows 7 VGA, I can get the HDMI output to work. But of course the resolution etc is not perfect.

If I install the catalyst drivers and reboot. I can see the BIOS screen come up, then the Windows 7 boot animation, and then the screen goes blank. Nothing more.

If I log in to the HTPC with logmein, Windows 7 says its detected the display as "VSX-520" and the resolution is set to 1360x768 (which is the correct resolution for the LG 42LC7D). I can't select/detect any other displays.

Any help please?

The amp is reporting a resolution of 1360 x 768, which is correct for the TV.

A direct connection works fine.

If i've tried the latest drivers, which ones would you suggest?

I've tried safe mode / vga only, and that works ok.