Like others, I'm just using an enormous iTunes library assembled over many years.
I still listen to lots of CDs, but it's very convenient to have my big, organized library and many playlists available all over the house.
Squeezebox by Logitech is no longer made but many used pieces can be found on Ebay that work perfectly well.
A pretty good alternative is to make DIY Squeezebox players from a Raspberry Pi board, Wifi dongle, microSD card, micro-USB power supply and (most importantly) the DAC of your choice and price range. Squeezebox software was donated to the community by Logitech when it closed down making units and it's still being improved. Each unit without DAC will cost about $100 bucks but you add the DAC of your choice and either amplified speakers or plug it into your amplifier.
Squeezebox server software is c/w Mac, PC, and Linux and runs well with iTunes.
It is compatible with hi-res music files.
There is now Raspberry Pi LCD touch screen so my next player will have one of those.
Here's 3 of the 6 or so players I built: