with cmss enabled the positioning will be enhanced more especially sounds that are in the vertical plane (something most sound cards arnt great at) especially with 2.1 speakers or headphones an xfi card will fake rear channels when downmixing most other cards wont
But that's not EAX, and thus it's not part of the original discussion topic is it? Further, vertical-plane placement can only be done if the app provides that data via EAX, so vertical-plane adjustment has no basis in reality for games that are not specifically written for EAX.
The basics are simple: for "enhanced positioning" to occur, the game must know that capability exists and be written to support it. There's no magic wand that
anyone can "wave" and suddenly your sound card knows up-from-down in an app that had no concept of it to begin with.
ps: you sure about fmod being entirely software ?
Notice the mention of "acceleration" - this is not EAX, this is acceleration (ie CPU offload) of voice playback. And again, this does not affect total simultaneous voice output, positioning, sample quality or provided effects.
The entire reason for FMOD's existance (and others like it) is to provide an equal sound quality experience for all users, regardless of sound hardware. That quality might indeed be less than what is possible with a true / full EAX implementation, but a true / full EAX implementation completely nullifies the ability to run on everyone's system.
Hardware acceleration can still be leveraged without EAX, just like certain features of CMSS. These are features that are game agnostic; they can legitemately be applied to any application whether or not that app was coded specifically for it. EAX is not the same; it only applies when applications are specifically written for it. The same goes for "positioning" samples within a vertical plane -- unless the game was specifically written to handle such a thing, no amount of external hardware can "make it up".