Just so I'm clear on what you mean by "source direct". You are a looking for a HTPC solution that will decode ANY source material without video pre\\post processing and output the source material color space (i.e. RGB 4:4:4m YCbCr 4:4:4, YCbCr 4:2:2, YUV 4:2:0, YUV 4:1:1, etc...) and resolution?
Well, to be explicit, My priorities are in this order:
1. Any 1080 (Blu Ray content only) is output as sourced. No color space (RGB 4:4:4m YCbCr 4:4:4, YCbCr 4:2:2) conversions, no frame rate conversions (24p, 60i), no deinterlacing.
2. Any 480i content is handled similarly (SD DVD)
3. As I don't have much confidence in the encoding quality of much of anythign else I can think of (video downloads, odd ball resolutions, etc.), I'm not worried about what the GPU and software does to/for them.
I want pristene transport of the BR content. HD-SDI out would be the icing on the cake. That said, I don't suppose there's a commercial PC based HD-SDI card that would do that? As I understand it, except for BR ISO's (not sure there) the HDCP is stripped during the ripping process so maybe that would be a workaround. HD-SDI->HDMI converters without munging the video into upstream high end VPs (that don't have HD-SDI already) are available.
If I can have pristene BlueRay that would be the main heavy hitter. After that SD-DVD (480i) without color conversion and deinterlacing would be #2 on the list.