Apologies not needed.

You're right. If you connect it only to speakers, he'll soon be embarrassed to find that he wants it everywhere. Then he'll kick himself for placing it in the ping pong room, 72 feet from the distributed audio system!

So be prepared!

If I'm seeing it right, all you need is a stereo audio cable to connect this to your house system. Of course, that doesn't mean that the volume will be at a good level. That's further research to do before installing the thing. I'd set up an appointment with him, to be done on a time and materials basis, checking what cables will work, if the output levels are good, possible hum (which might be helped by turning up the volume or adding a car stereo ground eliminator transformer), whether changing the volume on a pair of speakers run directly off the unit's amplifier also changes the line level volume.... all the stuff you need to know to just slap it in place.