www.sonicelectronix.com
Nobody has mentioned this site. I just bought a memphis amp and my audiocontrol line out converter from them. Fast shipping, and i'm pretty sure they are authorized dealers of everything they have. They say all manufacturer's warranties apply, so that means they are authorized right? Either way, they have a warranty of their own. Cheaper than most too, and they have a price match policy as well if they aren't.
Check 'em out, they treated me well.
Nick