As you are already thinking, a separate power amp is as much (or more) about quality of the power as about the quantity of the power. Much of our time is spent at power output levels well below the 75W mark (often even below the 15W mark). A separate amp has a much larger power supply, not to mention more robust individual amp channels and better cooling. As for speaker damage, clipping is probably the easiest way to hurt a driver - and it's easier to drive a receiver amp to clipping than a separate amp. Overpowering the speaker is possible, but that takes a very high volume level. Your ears may bring you to ease off on the volume before you get close to an "over-power" state (also keeping in mind that lower efficiency speakers are designed to handle the larger amounts of power required to get them to really high volume levels).