It's unfortunate you're having such a hard time. My old H/K stereo receiver was built like a tank. I ended up frying it in college once (got it fixed though).
I can't help but wonder if there could possibly be some climate condition in your area, electrical or otherwise that's causing these issues? H/K isn't perfect, but this the worst case of brand let down I've heard of. 3 separate units, all at the same time having multiple issues.

I've owned a lot of makes, and have yet to find the perfect brand in audio electronics. For my money, Yamaha makes very durable stuff. Not always everyone's cup of tea sound/performance wise though. But I've even had problems with a Yamaha unit, so they're not perfect either.

I was a Marantz man until my last unit crapped out. I've never owned a Denon, so maybe they're up next, but it seems every 3 years they go through a rough cycle quality wise.

Everyone has their turn I guess. Not that this is much consolation to you. Look on the bright side, you've got an excuse to go shopping again.