Get proper speakers - 8.5" drivers ($600) and a decent amplifier (Yamaha $250). This stereo will out compete any of these intelligent speakers.
Whats missing (except Alexa) is an auxiliary audio out that can be hooked up to existing system like the one I mentioned above. Google Home doesn't have it but it works with Chromcast add on. I personally use apple TV as my Airplay hub. So, about all that's missing is a microphone.
I simply do not understand - perhaps I am a minority - the argument and discussion around sound quality. There is no replacement in my opinion to a standard large diameter floor standing speaker. If I want to listen to music, I don't want any compromise - I want to be able to play it on my main stereo. Some people just don't care and they'll put music on their phone or some random bluetooth doodad. Why?