Help on outdoor audio receiver

Hi, I'm looking to get outdoor audio in my backyard. I kind of decided on polk atrium 6. I'll also use a chromecast audio.
What I'm unsure is what kind of receiver or amplifier should I use? It would be in the shed, with electricity already available.
I was looking at sony or yamaha stetreo receiver which I am familiar with but there are also amplifiers on amazon that cost half the price but I never used that kind of thing.
They look smaller and easier to install in a shed. What are the cons and the pros about those things?

Thanks