The ALC889A and ALC1200 with DTS Connect, DTS Interactive and/or Doldby Digital Live.
Gigabyte ALC889A with software can fully encode positional DTS for 3d games and general windows use. This is a function of the bundled software and I dont think it would work on Linux.
When buying a new PC one of my big concerns was sound quality and sound drivers. I did not want to buy a separate sound card and I wanted to use my home theater system. Unfortunately due to a hasty purchase some years back I somehow managed to buy a home theater system that takes Stereo In, SPDIF Coaxial In and SPDIF/Toslink Optical In. This means that to get surround my sound card must produce a DTS or Dolby digital signal with more than 2 channels. Also, the home theatre system only had a single Stereo. Some sound cards have multiple analog stereo outputs which plug into many stereo inputs on the home theatedr system which relies on the sound card to produce 3 or 4 analog signals.
In persuit of fewer cables, the important bit again: the sound card must produce a DTS or Dolby signal with more than 2 channels. Many sound cards will encode to DTS or Dolby but produce a stereo digital signal. That means you have stereo and in 3d games and it will not be positional sound. When watching movies the sound card will pass the digital signal directly to the sound card but it will not perform any positional encoding. Some sound cards will label this as "DTS" and "Dolby" which is deceptive.
For 3d games or any funky usage of winamp you PC needs to be able to encode DTS or Dolbly signals on the fly. Realtime encoding of DTS and Dolbly goes under the name of "DTS Connect", "DTS Interactive" or "Dolby Digital Live" and involves a combination of software or hardware to produce the multi-channel digital output. (Rember: A 2 channel DTS signal is not the same as 7.1. Many sound cards will perform stero encoding which is not what you want).
I bought a Gigabyte GA-MA78-S2H which has the ALC889A sound chipset and this implements DTS Connect and DTS Interactive and I get positional sound in games and music via my optical out. The software that comes with this Gigabyte mainboard is great and allows you to tweak all sorts.
One of the more impressive tweaks is to adjust the center channel which is usefull when you play stereo music on 5 speakers. Typically you end up getting all of the voice out of the center channel and its nice to distribute this across other channels by making the center channel wider.
Some websites suggest that the using DTS Connect and DTS Interactive takes 1-3% CPU power to perform this. I dont notice a difference so I dont really care. Dolby Digital Live encoding is supposed to be slightly more efficient to encode in software but I dont currently notice a difference so I dont really care - it works.
My experience with Gigabyte is good. Now although the ALC889A that is used on the gigabyte mainboard can fully encode DTS I believe that this is a feature of the gigabyte software. The ALC889A is a customised ALC885 and is made by Realtek for exclusively for Gigabyte.
One of the alternatives to Gigabyte was ASUS which also has an exclusive sound chipset from Realtek - the ALC1200. I did quite a bit of research and could not confirm that it is able to do DTS Connect. I would imagine it is more advanced because its version number is higher [How technical is that :-) ] but nowhere could I see any mention of realtime positional encoding of Dolby Digital Live, DTS Connect or DTS Interactive and they fall into the same trap where the mainboard supports Steria Digital encoding, will pass DTS and dolby signals from a DVD to your amp or will render the DVD digital to your 4 analog stereo outputs. Very Deceptive.
I dont think that this board will have DTS for linux since the DTS Connect / DTS Interactive has to be implemented by software drivers. In comparison, there has only been one "perfect solution" which was implemented completely in hardware. The nVidia Soundstorm along with its nForce 2 transparently produced full digital signals. This was implemented in hardware.