Audio/Sound/Volume Issues - Please Help

First off, let me qualify that I've spent a good portion of the morning viewing posts on audio and volume issues and found nothing specific to my problem. Also, accept my apologies if I've posted this in the wrong place, as well as my lack of technical expertise in this area.

My PC (Alienware Aurora) has been directly hooked up to my Vizio HD TV with an HDMI connection from my 5870 ATI graphics card (so both video and sound). The TV is, in turn, hooked up to a Sony receiver/amp that drives my home entertainment (sound) system via an audio optical out. this system has 5.1/3.2 capability. Using this setup, I've experienced no problems with the audio, other than the limitations prevalent in the game configuration audio.

I also run a direct spdif optical connection to my recevier/amp from the PC motherboard (sound card), for whatever reason this is the only way I can get blue ray sound, which is a whole other issue, I believe specific to Dell's proprietary Power DVD.

If I play ffxiv with the spdif audio connection, I get dramatic spikes in my audio, specifically, weather, fireworks, spells, WS, etc. painfully reducing the music volume.
Also, a near constant wind sound no matter where I am, no matter if it's windy or not. With the HDMI hookup, I didn't experience this problem at all.

Recently, my receiver/amp has been acting up so I disconnected it and while I'm planning another amp soon, I'm now playing this with the HDMI hookup, but with non Dolby Digital sound directly from the TV. When I do this I experience the same sort of background sound issues that I do with my spdif connection, even though the sound is driven by the 5870 sound card, not the motherboard soundcard, as would be the case with the spdif connection.

While all this is very annoying and detracts from my game experience, it's a liveable situation, that hopefully goes away with the new receiver/amp. However, I was hoping someone more technically astute might see a solution to this problem. The audio options in game don't solve the problem. I didn't notice anything in the ffxiv system configuration that would fix this issue, so I'm assuming any adjustment would have to come from PC/Windows/5870/etc.

If anyone can provide me some technical guidance in this regard, I would be sincerely appreciative.

Regards.

If you use the HDMI output for sound you will only have stereo sound with games since only PCM encode is supported. For the optical output it depends on the soundcard settings. Some soundcards require to use the "speaker" output even if you want to use a digital output (ASUS Xonar) and set it up to use the dolby encoder. Realtek HD Audio chips don't need you to use the "speaker" output but you have to set the audio output format to "dolby digital live".
If the dolby encoder is bad (or even broken) there can be issues with the loudness of 3d sounds in games.