Audio Production w/HDMI underrun issues

Hey all. This is my first post on the site, but I constantly turn here for advice. I've been a music producer for about 10 years (hobbyist- not pro) and I just built a new rig (my first build ever) for better audio production capability and some gaming. My components are as follows:

NZXT M59 Case
Gigabyte GA-880GA-UD3H Mobo
AMD Phenom ii X4 955 Black Edition processor (running stock fan- stays rather cool)
Sapphire Radeon HD6790 Graphics card
Ultra LE 650 watt power supply
Corsair XMS3 Ram (2x2gb)
Asus litescribe 24x burner
hitatchi 7200 rpm 500GB hard drive
Windows 7 Home Premium 64-bit

I'm running the whole system via HDMI (from my graphics card) into my 42" Vizio VO420E TV (with a surround sound system plugged into the TV). It bears mentioning that I DO NOT have a dedicated sound card in my system because the Radeon HD graphics cards have onboard sound support through the HDMI. Now for my question-

I am getting some buffer underruns in FL Studio 8 (annoying crackling and popping noises when the minimum sound buffer is exceeded), and I had to set my buffer length a full 10ms or so greater than on my old Pentium D machine. This makes no sense, because everything in my new rig beats the pants off my old one. But I figure it could be the fact that I am running the audio and video through the HDMI. I can't seem to use the RealTek audio options at all though. I selected the RealTek HD audio in FL Studio, and the Windows 7 playback devices screen indicated that there was a signal going through that channel, and even though I had a 1/8" cable running into the TV, I got no sound. In fact, I played with all the settings for the better part of an hour, and no combination of other settings gets any sound out of my system EXCEPT the HDMI setup. I can't seem to disable the HDMI audio ONLY and still use the HDMI video. What I noticed though, is that I can set my buffer length unbelievably low while using the other audio systems, I just get no actual audio. I am wondering if I should try hooking up a VGA cable to the back of my TV and jacking the audio in directly, to see if that makes a difference. Both my computer and TV support optical, but I've never used optical audio before, so I don't know if that's a valid option.

My question is this: Is my HDMI cable the potential cause of my buffer underruns? And if it is the cause of my problem, what can I do? Should I use an interface? A dedicated sound card? Just need some advice on this one, and thanks in advance!