I have the Gemmy Lightshow box, 6 outlets, with mp3. On the bottom of the control box next to the electrical cord and Speaker RCA jack port, there's a round, green screw-on cap cover which is labeled "Link Port". Gemmy's instructions on using this product aren't very helpful and do not mention the purpose of this port--looks like some male connector of sorts. I've been to the Gemmy website and even when you enter the item number into their Advance Search option under Customer Service on the site, nothing comes up. I figure someone here will probably be better at giving me help anyway so here I am asking! Anyone?