I used the same exact thing for about 5 years and LOVED it.
I recorded on 22 tracks (2 for each room for stereo) and had each channel go to 11 different home stereo 5.1 systems. Then the speaker wire was ran to each room. All the audio systems were in one location in the back room which made it very nice.
On the back of the ADAT I had a "Y" audio 1/4" connector going from two channels to a single connector plugged into the "AUX" input on the home stereo system. From there is was the stock speaker wire and speakers (that came with the stereo units) put in each room. 6 speakers for each room for a total of 66 speakers.
I just turn the power on and hit "play" and it loops all night.
BTW, I used it for different background music/sound in each room.
Very simple to use.
Hope this helps,