the intel HDA audio chipset and the nvidia sound storm 2 chipset carried out dolby digital encoding in real time, and could output multichannel audio from games along the spdif as 6 channel dolby digital.
not sure if anyones using the Intel HDA chipset in soundcards though.
EAX2 was an open format to get developer support. EAX 3 onwards (up to EAX HD) is proprietary to Creative, so there won't be any other cards that support this feature than the Soundblaster line. Having said this, consoles have been running games without EAX for some time and they sound fantastic. I can only assume that the CPU's do much of the sound processing (isn't it all software for the '360?) so hardware EAX acceleration may not be such of an issue in the, admittedly far, future.
The HDA cards are good with flawless 5.1 output, but they have poor upmixing from stereo unless they have DTS Connect capabilities, and even then it isn't as good as PL2. I would also say that the software is a bit hit-and-miss until you get used to it, whereupon you wonder why Creative insists on dumping a few hundred meg of bloatware on your PC in order to get the most out of their cards.
Yeah, the original version of Doom3 did all of its environmental audio processing on the CPU, and sounded great with either 6 channel analogue output or when running that through a dolby digital encoder (didnt try the HDA stuff, but the soundstorm did a great job with it when it worked).
Why upmix from stereo? Surely it would be a better idea to leave that alone and output the basic stereo PCM from the card to a processor to do PL with?