Karajorma, what I'm referring to is not EAX but the competing technology at the time also supported.
It allowed pseudo-surround sound with 2 speakers, just wondering if support is still there.
Uh, sorry but FS2 never supported anything other than EAX and DirectSound. Competing technology to EAX would have been Aureal A3D which didn't succeed. At least I don't remember there having been anything related to SRS in FS2 retail.
However, technologies like SRS Headphone, TruSurround XT, TruBass, FOCUS, SRS Virtual Surround, Circle Surround, SRS Wow, Dialog Clarity, and VIP can be used if licensed. Naturally they expect money (lots of it) in exchange for a license. Even then you'd need to use externally linked libraries because I doubt you can bundle them within FSO executable due to incompatible licenses.
You would have to find free alternative that has license suitable to use with FSO. And that'd be OpenSL.http://www.khronos.org/registry/sles/specs/OpenSL_ES_Specification_1.1.pdf
Unfortunately there is only one implementation of OpenSL, the ES (standing for Embedded Systems). So there is no equivalent for PC's like in the case of OpenGL vs OpenGL ES. Prominent video card drivers from AMD, NVIDIA and Intel do support OpenGL ES too (at least up to v2.0 iirc), but I have no idea whether PC audio drivers supports OpenSL ES.
And speaking of externally linked libraries, I wish SCP would use OpenAL Soft by default as they could bundle it within FSO executable. Thus removing the need to have Creative's OpenAL as prerequisite to run FSO with working audio.