I'm running an AMD A6-3670K on an ASUS F1A75-M PRO/CSM (I was shipped the Corporate Stable Model free of charge) and it serves me perfectly fine running on-board Realtek Audio connected via HDMI to a Yamaha HTR-6260 receiver. In fact, I had used on-board audio on my previous HTPC build 18 months back and it was crystal clear (no hiss) as well. Even the Zotac ZBOX Nano AD10 that I ran in-between builds did a solid job of HD Audio via HDMI.
On-board audio, when ran digitally, has come a long way from the old days.