You should NOT be connecting more than one set of speakers to the speaker terminals on the amp. We did that at McDonalds when I worked there and amplifiers don't like that one reason we went through many receivers over two years. Of course they blew with one set too because aparantly JVC Sony and Yamaha didn't like running 20 hours a day at moderate volumes.

The volume on the speaker has everything to do with sensitivity of the speaker and NOT the wattage. Most people don't understand that watts are indierectly related to volume level and most of the time totally irrelevant.