Yeah, the AGP Hotfix are essentially the same but with the AGP models included in the setup script. I suppose it saves AMD some expense in not certifying and/or Microsoft no longer does so for AGP -plus it shifts the ultimate support responsibility to the card manufacturer.
As for the PSU, check the label or otherwise look up the model number to confirm the 12V amperage but, again, I doubt that is the issue.
DirectX version 9.0c could potentially not be current as it does not specify updates -the latest package is "directx_mar2009_redist".
Mainboard manufacturers do not necessarily provide the latest drivers so check with SiS. The chipset is often the culprit with a variety of problems. It is really best to stick with Intel or AMD as third-party ones are often dodgy -although more problems are heard about Nvidia and VIA than SiS but that could be due to volume of sales.
I would stick with a 3650 rather than 2600 anyway (I've had both). Sorry, I am not familiar with TMT and did not realize that the trial did not work for BD but what about file mode? Does the same problem occur with files? Does it occur with all video codecs (AVC, VC-1, and MPEG-2)? Oh, PDVD 8 decoders may not work in MPC-HC (those from 7 do) but you can try the MPC-HC internal decoder anyway.
Have you tried toggling hardware acceleration on/off? Run the DirectX Diagnostics Display tests? Check CCC SmartGart results/settings (this could reveal potential chipset problems)?