Need suggestions for streaming files to my stereo

Free Solution:
You have a Google Chromecast Audio, so use it.  Download and install Google Chrome and enable Cast.  Then you can Cast the Desktop Audio to the Chromecast.  However, it doesn't work with iTunes.  A work-around is to upload your iTunes library to Google (first 50000 songs free).

If you had an Android phone, you could use BubblePNP and just play the music stored on the phone. This is what I do.  I stuck a big ass micro-sd memory card in my phone and carry around a lot of my favorite CD's including some Hi-Res.  When they announce 2TB micro-sd, I'll be the first to pre-order.  Then I can fit my entire music library on the Phone and dump the music server.   Again, iTunes not supported.
https://support.google.com/chromecast/answer/6279396?hl=en&vid=0-1189761614155-1502287144843

Another option around your budget is a device based on Play-fi.  I occasionally see the Definitive Tech or Polk Play-fi devices on eBay for $150-$250.  Sometimes a Paradigm unit pops up in that price range.  Play-fi supports 24/192.  Also, it has dual-band WiFi for all those people above.  I have two Def Tech W-Amps driving my Living Room and Dining Room.  Play-Fi supports DNLA, so it should see the media on any shared directories on your network.The App has come a long way and matured nicely.  

If you could stretch your budget, then +1 on Auralic Aries Mini.  The Mini is a self contained solution; stick a 512GB SSD in it and it's both Player and Server.  

Again, if you can stretch your Budget, then +1 on Bluesound Node 2.  I've seen them come up on Ebay for $350 new.  The Node supports 24/192 and MQA.  

A little off topic, but for those running Squeezebox Server, there’s a plugin to allow a ChromeCast to emulate a Squeezebox. A few little problems with Sleep/Wake on SBS, but other than that, works pretty good.

If you’re thinking about a dedicated Server, and don’t want to full around with a Pi, there are many Tiny PC "Bare-Bones" kits available. Some are even passively cooled. Some to think about are Intel NUC, Gigabyte Brix, Zotac, Logic Supply and Compulab. Also, some NAS will run Squeezebox Server, Kodi, Plex, Bubbleup and are DNLA compatible.

For years I used a Compulab fanless Fit-PC. I then went to Gigabyte Brix Fanless. Switched to a NUC to take advantage of M.2 NVMe SSD. So glad I made the switch to M.2 because backups, updates, indexing is soooo much quicker now. Yes, I know it’s way overkill for a server.

Sorry for the off topic side trip,

The problem with using Logitech Media Server is how much longer is it going to be a viable option?  Logitech stopped supporting it a few years ago.  It is open source, and the people over at Slim Devices have kept developing it.  As time goes by, and there are fewer and fewer people using Squeezeboxes, the development is going to drop off.  So, how much longer do we have? 5 years?  Maybe 10?  The original Squeezebox debuted 16 years ago.  One good thing is that Logitech has the SlimServer up and running.

So, if you want to try something free and cheap, then you could use your CCA with LMS.  Just keep in mind that eventually it's going to become an orphan product.  Though, based on home much money you would have invested, it's really not that hard to move on.

The problem with all these Players/Options is that things are just moving too fast.  You buy into a Streaming Ecosystem, and in a few years, something better, easier, faster comes along that supports even more services and better sounding/higher quality audio formats.  The question is when do you jump on the Merry-Go-Round?  Who long do you stay on, before jumping onto another ride?  Enough with being cynical...........

The latest build of LMS is: 7.9.1-1502265250.
The last version supported by Logitech is: 7.7.5

Autre,

I think you misunderstood my previous post.  I wasn't advocating against using LMS, I was just pointing out that it is not a long term solution.  And, with only $35 invested in a CCA, it's not really that big a deal if it stops working in 5-10 years.  I'm sure by then, you'll have saved up enough to move on to something else.  LMS can run on just about any computer running Windows, MacOS or Linux.  So, if you have an old laptop or PC sitting around the house, put it to use.  After all, if you don't like it, the most you loose is a few hours of your time.

Let me explain what the SlimServer is.  It's a Server, maintained by either Logitech or Sean Adams, that hosts. mysqueezebox.com.  Mysqueezebox.com allows Squeezebox users to do two things.  First, it allows you to use you Squeezebox for Internet Radio, Pandora, etc without having to install LMS on a local computer; it stores your account info.  Second, it provides the clock information for the clock screensaver.  So, if Logitech were to shut it down, then you would need LMS running on a local computer to use these services.  I believe that most Manufactures of Streaming devices maintain a Server to store basic account info.  I know that Sonos, Google, Amazon, Play-Fi, Hoes and Bluesound all do.  At least, all the different units that I've tried/own do.  Since the CCA would only be using LMS to "serve" your music library, then you'll never have to use Mysqueezebox.com.

On a side note, you don't have to use LMS to "serve" your music.  There are many other software choices such as Kodi, Plex, BubbleupPNP, etc that do the same thing.  It all just depends on your comfort level with setting them up.

Finally, thanks to Thunder240 for providing the instructions for the Raspberry Pi.  You don't actually need the HifiBerry card because you will not be plugging any audio devices directly into the Pi.  Complete kits can be purchased on Amazon for $70 with a 32GB memory card.  You will also need an external USB drive to hold you music files.  A 1TB drive can be purchased for around $60.  Keep in mind that the Pi only has 1GB Ram and is pretty slow, but perfectly fine for a server.  A Intel NUC5CPYH kit or a Gigabyte GB-BXBT-2807 kit with 4GB Ram and 128GB SSD or 1TB mechanic drive can be had for around $200.  You would have to add an OS.  Windows 10 can be purchased on Ebay for about $60.  If you want to go with something a little bigger, then a  HP ProDesk 400 G3 Mini - I3 6100T Reburb can be purchased for less than $300 with Win10 and 500GB drive though I really recommend an SSD.  

I hope then Thunder and I are not confusing you with all the options,

You'll have to use a Flavor of Linux that supports ARM CPU's.  As for which one to use, I'll defer to thunder240 to answer that question.  Also, JRiver is Playback Application, not an OS.  JRiver is available for Linux.  If you're planning on using the Pi plugged directly into you audio system, you'll need the HiFiBerry kit.  Then, you would use an Application like JRiver to play music.  Many people swear by the Roon Player, but it's pricey at $119/yr or $499/lifetime.

If you're planning on just using the CCA as the Audio source, then all you would need is an Application like Plex, Kodi, etc to "serve" the music files to the CCA.  If you go this route, once the Pi is setup, you can run it headless; without a monitor.  You would use another computer, or tablet/smartphone, to control the Pi remotely for occasional maintenance, changes to settings, etc.  My Music Server is actually mounted on the wall right next to my router.  I use my main computer to control it remotely for occasional software updates, maintenance, etc.  Also, I use the LMS web-portal to control my Squeezebox Touch, which by the way, is sitting right next to me; it's easier than using the players own interface. To use the other Squeezebox devices located throughout the house, I use an app on my phone.