Grace Digital Audio has designed a custom dock for the Fire. 16-Watt amp, 3" full-range x 2 front bass speaker system, remote control, optional rechargeable battery. Usable either vertically or horizontally and is capable of charging the Fire while using it. Good chance it may be a bit pricey but this is no ordinary dock. Nice looking too.
Details here (scroll over the thumbnails for various views):
Grace FireDock