Xpantastic!

Hi Folks,

I recently noticed an XLR socket the far left of my Xpander, with a 
little black on/off switch beside it.

I took photos of the inside and outside of my Xpander:

http://sanfransys.com/photos/xpanderxlr/xp_internal_1.jpg
http://sanfransys.com/photos/xpanderxlr/xp_internal_2.jpg
http://sanfransys.com/photos/xpanderxlr/xp_external_1.jpg
http://sanfransys.com/photos/xpanderxlr/xp_external_2.jpg

Does anyone know what this might be?

Thanks,

Jeremy.