ACX is the distribution network that will put your book into Audible, Amazon, and iTunes. Findaway voices will push to ACX, but if you submit directly through ACX, the royalties are higher. The Audiobook market is still emerging, and this is the best place for authors to be, but the cost barrier is high. ACX helps by connecting you with narrators and producers who will produce the book for a cut of the royalty instead of being paid upfront.
Besides just listing the books with the three audiobooks sellers, you will also get an affiliate link where if someone signs up for Audible using the link connected to your ACX account you will receive a bonus referral payout in your royalty report.