Using one set of speakers with AV receiver and Lamp amplifier

It may work. What happens if you are listening to your tube amp,and you accidentally sit on the HT receiver remote and power it up?? I’m not a tech,but I’m guessing this would not end well.  Why take the chance? 

You can but something is going to fry. Your amp will be feeding your loudspeakers and your amp. Not designed to do that. 

I don’t think so.

If you only keep the B&W speakers ,
You need something like this :

What is a lamp amplifier? Your question doesn’t make much sense. Can you elaborate