Having worked 7 years as a repair tech, including custom DJ equipment, I can attest that power transistors are by far the most common point of failure in amplifiers, but no surprise there really if you understand how they operate.\n\nI think one of the biggest argument for per\/pros is the power supply as TLSG mentioned. If you want to drive 13 channels at rated power and still have stable power for all of the delicate electronics, you really need to separate the amp section. A power supply that could maintain rated power output with all channels driven would make an AVR huge and heavy. Manufacturers are making compromises knowing that most people don't push their AVRs to the limit or they won't notice that power is slightly degraded when switching from 2 channel to 13 channel listening. All the more reason to get that extra 40 or 50 watts per channel so that you can make up for the change in performance with all channels driven.