3 sets of speakers

Hi there, a friend of mine needs help on the following:

He has a pair of JM Labs floorstanders in the living room, a pair of same brand monitors in the dinning room and another pair of monitors in the terrace.
He's currently powering the first two with a sansui 2 chnnel receiver from the 90's, those with A+B speaker selectors.

Whats he needs is a form of amplification that would allow him to have different volume settings for each pair of speakers i.e. that he could be rocking outside and have the same music but with a tolerable volume on the dinning room.

I guess a 3 zone 3 channel receiver would do the trick, if I'm not wrong Marantz makes one delivering 40 wpc which I guess is enough.

What do you recommend, the cheaper the better.

Thanks !!!