Well, I do have an A8 Llano HTPC and it's awesome, but found out it was actually a little overkill for HTPC.
You could settle with an A6, since applying most of post processing effects won't miss a Stream Processor.
One word of advice with Llano though. It's annoyingly picky with RAM settings; I had to change the Kingston HyperX modules for Corsair Dominator ones for it to work fine (no idea why). It really makes "good" use of RAM, so, don't be that "cheap" when looking at RAM modules.
In a positive light, the Asus MoBo for the A8 I have is wonderful. I know "cheap" Intel MoBos are not, so it's up to you.
If space and MoBo "quality" is not a concern, then the G620 will do fine with a good video card. AnandTech has a very good review for HTPC video cards, you could go check it out.
Cheers!