You can place 512 sounds max. with the choice of 9 (or maybe 10, don't remember) different sounds, not 9x512.

The best way to add sounds is to use dedicated objects because you can place them exactly where you want. Forget about the pits, stands, etc...
The sound level when you are on the track is very low, so don't hesitate to push the level of the wav file very high.
I had many crashes when living the track (the session) when i use other thing than 8 bits 22050hz stereo (or mono). I still have some crashes with that but not very often.

When i tried to use a flat polygon object as source sound, it didn't work. So i used cubes ( an exemple is included in the zip file with a transparent texture). 
When you place the sound object, put it very close to the track itself or you won't hear it enough. For the height, i used 3 meters so you can hear the sound below it too and like that, no possible collision bug problems ( even if the object has no collision properties).
One sound source object is clearly not enough. You even don't have the time to hear it when you drive. For exemple, i use 3 objects for the Urbanya waterfall.
Very important too : if you want a good linear sound, you have to separate the objects from 15 meters. Less is useless. If you add more, the sound level fall down and you will have an horrible wha-wha effect between them.

Hmmmm what else... Ah yes, i used big 3do cubes so i can easily see them in 3doED. When all is finished, you just have to resize them to something smaller. Only the X,Y,Z translation coordinates are necessary in Racecon. Don't bother with rotations.

Well, i think i told you all that i kwow. Sorry if it's not very clear   

Ciao !
Jack