Feature Request: STR Support

[mattlathrop]

Hello!
I have an Anthem STR and this integration seems close to supporting it. The connection works fine, I can even change inputs and volume which is all I really care about. However there are a few bugs:

• When HTB is enabled RCA4 is not selectable perhaps a different string/name needs to be passed?
• Volume works poorly from home assistant. The STR uses a -96.0 to 7.0 scale which the percentage didn't map well to.

I've built some integrations with the STR for Roon so I am going to take a look at fixing these. If the author/community has any tips/advice to share as I start looking or wants to assist please let me know!