I've a B-series and have seen no DHCPv6 configuration. I posed the question to D-Link tech support several months ago as to whether they were planning to release a future firmware version that supported IPv6. However, they said "no official plans" for it.
Now, all should realize that the DIR-655 is intended as an inexpensive home not an enterprise product and probably not the ideal product to use for anything larger than a home business. Perhaps a DSR-500N would be more fitting - more costly but as a business a tax write-off may be possible. It is in same price range as a 10-user Cisco ASA-5505 but has Wireless-N as well as gigabit. Unfortunately no documentaion of its processor, memory, and precise detail of its supported capabilities.