Thanks for your input. But I have no clue if making a thousand Source Voices, each with its own submitted pAudioBuffer has any negative consequences.
The question is do you need that much polyphony? I was able to survive with a pool of 32 tracks, as each sound effect only lasts a short while (1 sec or so). If your 1 effect requires 5 sounds, why not just preprocess them into 1 sound clip, and play it all on the same source voice?