You have it all figured out, sounds like what you are going to do will work.

I will say this however - I would NOT sell him the equipment.
Having live instruments plugged into a 'non pro audio' sound system, is a disaster waiting to happen. Even if his mixer has the appropriate DSP (compression, limiter, subsonic filters, etc.) to keep from blowing out the consumer equipment. There is no guarantee he or whoever touches it, knows or understands how to use it properly. One performance with the wrong setup and kiss those speakers and/or amp goodbye - TOAST!

If he wants to play mad scientist, make sure he does it with his equipment and with his dime. You just get paid your time in hooking it all up properly. The little extra money on the equipment is not worth the nightmare that could happen from this one day, if someone is not careful or doesn't know what they are doing while operating it.