Any cheap ass mobo will do i would pick one that was passive cooled and got everything you need.
same go's whit mem, just take the cheap mem, size is more important speed.
For PSU take any whit silent 12cm fan.
If you would like to also be able to play game's i would pick a faster CPU instead of all the problems whit overclocking and would also pick a (faster) passive VGA card
For CPU cooler i would pick the
Noctua NH-U9F its the best cooler that fits almost any full size HTPC case and will keep any CPU cool but dose it also very silent.
Remember when your building a HTPC silent is golden and any part you pick should first be selected on noise emissions above anything else
