It doesn't make the Yamaha limited to 40 wpc unless equal demand is made of all 7 channels, which isn't likely. I'd just use the avr until you have some obvious issues, doesn't even sound like it's all setup yet. If you really want to buy some amps to see if it makes a difference, there's one way to find out

. The 5000 is nice for the price, tho I'd probably just get a pair of Crown XLS1502s and get much more power for about the same money.