I can report it's all working as expected now - seems I shouldn't do these things over a remote link.
I re-made the inf file (attached in zip) using the first block from my Pioneer 435XDE and the second block from the live view (using Moninfo).
Once I'd done that and reloaded the inf against the monitor, ATI drivers now report a combination of a Pioneer PDP and the Denon AVR. The combined settings show up as HDMI, so I got all the nice scaling options back, no more pissing about creating custom resolutions either.
I set up the audio and tested it out with a few different blu-rays, all work as expected from PowerDVD. PowerDVD will still either re-sample the audio if you select it to use 6 (or 8) speaker output. If you choose the HDMI output it will either output the full basic DD or DTS for DVD/blu-rays but only the core DTS from blu-rays encoded DTS HD Master Audio. Didn't try Dolby TruHD but I'm 99% sure that's the same, you only get the core. Still seems like Cyberlink need to work on the PAP. There are of course other options than PowerDVD to get the full output...
Anyway, enough rambling - here are the two important lines I replaced:-
HKR,EDID_OVERRIDE,"0",0x01,0x00,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0x00,0x11,0xEE,0x12 ,0x00,0x01,0x01,0x01,0x01,0x00,0x12,0x01,0x03,0x80,0x50,0x2D ,0x78,0x0A,0x0D,0xC9,0xA0,0x57,0x47,0x98,0x27,0x12,0x48,0x4C ,0x20,0x00,0x00,0x01,0x01,0x01,0x01,0x01,0x01,0x01,0x01,0x01 ,0x01,0x01,0x01,0x01,0x01,0x01,0x01,0x01,0x1D,0x80,0x18,0x71 ,0x1C,0x16,0x20,0x58,0x2C,0x25,0x00,0xC4,0x8E,0x21,0x00,0x00 ,0x9E,0x01,0x1D,0x80,0xD0,0x72,0x1C,0x16,0x20,0x10,0x2C,0x25 ,0x80,0xC4,0x8E,0x21,0x00,0x00,0x9E,0x00,0x00,0x00,0xFC,0x00 ,0x44,0x45,0x4E,0x4F,0x4E,0x2D,0x41,0x56,0x41,0x4D,0x50,0x0A ,0x20,0x00,0x00,0x00,0xFD,0x00,0x31,0x3D,0x0F,0x44,0x0F,0x00 ,0x0A,0x20,0x20,0x20,0x20,0x20,0x20,0x01,0x88
HKR,EDID_OVERRIDE,"1",0x01,0x02,0x03,0x45,0x75,0x5A,0x85,0x04,0x02,0x03,0x06,0x07 ,0x10,0x0E,0x0F,0x0A,0x0B,0x23,0x24,0x14,0x13,0x11,0x12,0x15 ,0x16,0x1F,0x1D,0x1E,0x19,0x1A,0x25,0x26,0x38,0x09,0x7F,0x07 ,0x0F,0x7F,0x07,0x15,0x07,0x50,0x3E,0x1F,0xC0,0x4D,0x02,0x00 ,0x57,0x06,0x00,0x67,0x54,0x00,0x5F,0x54,0x01,0x83,0x5F,0x00 ,0x00,0x68,0x03,0x0C,0x00,0x11,0x00,0x80,0x21,0x00,0x8C,0x0A ,0xD0,0x8A,0x20,0xE0,0x2D,0x10,0x10,0x3E,0x96,0x00,0x13,0x8E ,0x21,0x00,0x00,0x18,0x8C,0x0A,0xD0,0x90,0x20,0x40,0x31,0x20 ,0x0C,0x40,0x55,0x00,0x13,0x8E,0x21,0x00,0x00,0x18,0x00,0x00 ,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00 ,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x5E
Due to the limitations of the posting, please note that the long string of numbers is on one line for each entry, there are no carriage returns etc.
The second line is the important one for Denon 1909 users. The first one being of course from my Pioneer 435XDE. That's the one you'll need to replace to get your own customised setup.
If you use EnTech Moninfo, you should be able to get the EDID from the registry value for your monitor/TV to insert. If it doesn't appear then you'll need to hook the TV up directly to the graphics card and get a live reading from Moninfo and then swap back to the Denon.
To save anyone the hassle of typing a lot of numbers and adding 0x to 128 numbers, small tip is to use find and replace in notepad - search for a , and replace with ,0x
One little caveat for you - I don't think this will work under Vista x64 due to the unsigned driver restrictions. I'm not using it to test it. I am aware that MS recently changed their policy and now allow unsigned graphics driver to go on OK, but no idea on monitor drivers.
Let me know how you get on!
Denon_1909.zip 0.970703125k . file