This is all a bit odd.
ADM's offer a simple minimal box solution for relatively simple systems, if you really need more input facilities and switching options, buy a proper preamp and some more conventional active speakers, should you wish to go down that route.
I know that AVI have, in the past, supplied pairs of 'slave' speakers, with just a single input and nothing else, but I believe they are generally reluctant to do so, simply buy something else, there are plenty of good active speakers out there if you can be bothered to look.
I have been very tempted by a pair of Adam Artist 6 floorstanders with a BK XLS400 sub, this combo can be had for the price of a pair of Red Spot ADM's and a pair of decent stands.
http://www.adam-audio.com/en/multimedia/products/artist-6/description
http://www.bkelec.com/hifi/Sub_Woofers/XXLS400FF.htm