In time the full soundtrack will be released and available for purchase.
Yeah, I imagine once all the bugs have been squashed and Kirill is back to full health then they'll release a definitive soundtrack to buy.
What location(s) are you at that you get to hear this one musical track? Maybe we can help you narrow it down to the song you like.
I've mainly heard it outside of Cyseal, in the wilderness. It's like a really ominous sounding song; it sounds really haunting, and as it goes along an accoustic guitar starts joining in very softly, and then after that a male choir starts to sing along, too. For some reason it reminds me of Adagio for Strings, but only very slightly.
I'm just wondering if it's new material, or if it's from a previous Divinity game. I don't think it's from Divine Divinity, but I'm not positive.