Main Zone not Working

VERY nice system! But, it practically needs a cooling system of its own! So, the very FIRST thing to check is to make certain there is plenty of OPEN SPACE around the receiver. SECOND: Make certain ALL of your speakers have an IMPEDENCE of 8 OHMS. (Denon says 6 ohms is okay; I still recommend 8.) Virtually all speakers of even modest quality will include this specification on a label on the back of the speaker. You CANNOT run more than (2) TWO speakers with 4 OHMs impedence on ANY amplifier (technical discussion too long!) [NOTE: Your Denon's internal overload protection system is designed to do precisely what it is doing, to prevent permanent damage. In general, shutting-down, then re-powering the system after several minutes usually resets it. However, if there is a problem, this will continue, AND YOU RUN THE RISK OF DOING SERIOUS DAMAGE TO THE MACHINE!] Before you take this monster in for service, there is one more "test": check for shorted and/or mis-connected/disconnected speaker cables/wires. With as many as 22 speakers connected, this could take some time. But it MIGHT be worth it. 1) Visually inspect connections at the receiver and speakers first. You might find something obvious! 2) If everything looks okay, then disconnect ALL of the speakers; and reconnect and test them one at a time (at relatively low volume.) For example, reconnect the left front speaker, test the system; THEN add the left front, test the system,and so on, ADDING one more speaker each time - FIRST MAKING SURE EACH OF THEM HAS AN IMPEDENCE OF AT LEAST 8 OHMS! IF there is a short (or bad speaker) this will help isolate it. Denon is a very respected brand, and will give you a LIFETIME of service. Hopefully one of these simple fixes will work for you. GOOD LUCK!