I have yet to use a 9813... but I know you'll be more than happy with a 7894... I dont think the 9813 adds enough features to warrant the extra money spent.

For powering up the deck, you can run a wire to the battery... all you need is the power wire you mentioned and another fuse holder and a 20 amp fuse within 12 inches of the battery, these can be found at an auto parts store. There is also a customer access power tap on the top of the interior fuse box that can be used... there are 4 or 5 recessed terminals... one of which has constant power that the deck needs.