tapping into openal output possible?

i am interested in porting our HRTF library with openAL and testing it with the various games out there.

In the first instance, i'd like to simply tap the output of the sound card and create virtual 5.1 or 7.1 sources with 

individual HRTFs and headphones.

So my question is, is it possible to take the output of openAL, work out which speaker the source or buffer will be send to?

then I can add my filtering code there.

I can't seem to find what i need looking at the source or buffer properties, as they don't specify which speaker/channels

it will be played in.

cheers

/j