Updated Mac, advice needed on shared content and Sonos

I recently had my 2015 iMac upgraded. This included the removal of my 1TB hard drive that was replaced with a 2TB drive. I still have the 1TB drive and it is connected to the iMac via a dock. The dock also contains a 6TB drive that I want to fill with rips from my DVD collection, so that I can get rid of my physical DVDs (but that's another story).

The old 1TB drive had two user accounts - one for me and one for my partner. We both had iTunes content under our logins.

On the 2TB drive, there is only one account - me.

However, by using Finder I can still play her iTunes content under the new, sole login.

I know I can easily set up an account for her on the 2TB drive, but where should her music be stored so that every new purchase she makes on the store goes to the same location? (I don't think I've done this correctly when I moved my iTunes content over - I recently thought I completed the job properly but the next time I imported some CDs, there were folders of the artists a level 'back' from where I thought they'd be in Finder).

Then we come to Sonos.

We used to be able to combine both iTunes libraries and play them over the four Sonos speakers in our house. Can we still do this?

Any help appreciated, thank you.