Bests way to connect two input sources to one set of speakers?

One source is a stereo amplifier. The other source is an A/V receiver. I use the A/V receiver when watching movies. I use the amp when listening to music. I have one set of speakers and I am looking for a convenient way to connect them. I would prefer automatic switching, but manual switching would be OK if that's the only affordable option.

I heard about the Niles SPK-1 but it does not seem to be manufactured any longer. What are some recommendations?