Yes, it is. It's a bit of trouble but I zip the whole audio book and then add the zipped file to Calibre. Then use FBReader or the Calibre internet url or a Calibre app to transfer it to the Kindle. You can unzip it with Es Explorer on the device.
I like Ambling BookPlayer Pro to listen to audio books - even has a sleep timer. I even paid the outrageous price for the Pro version.
Edit: Just noticed you asked about Kindle Fire HD; it should work the same as on my Kindle Fire.