For this, you could use something as simple as this from Amazon, if you don’t already have RCA outputs, to convert audio out to RCA via USB on your PC and then plug it into an input on the Matrix Amp. And then you can use something like System Bridge to integrate the PC with HA to have some level of control over it via automation.
For me, I have an Echo Dot with a 3.5mm to RCA cable plugged into the Matrix Amp and can use it in automations to play media from Amazon Music and Pandora via that device. You should also check out the Music Assitant addon for HA that supports several streaming services and can play media on some HA media players.
I also have a 3.5mm to RCA cable from my HA NUC box to the Matrix Amp so I can use like VLC Telnet to play media from HA, like doorbell sounds and announcements via CloudSay.