You said your speakers are KEF 104.3. I don’t think they ever made a 104.3. If you meant 104.2, than they are an excellent speaker and would be hard to improve upon without spending a lot. I myself have KEF 104.2s. I have had many speakers over the years and they are still one of my favorite speakers. If you haven’t done it yet, they will need some refurbishing to sound their best. Over time, the ferrofluid drys out in the tweeters and needs to be replaced. KEF actually recommends doing this after about 15 years. This is a simple job and only costs about $10. Also the foam donuts and possibly surrounds, if you have the biwire version, in the bass drivers may need replacing.
Regarding streaming, I don’t use any internet music services but I did do free trials with Amazon, Qobuz, Tidal and Apple. What I do is stream my lossless ripped CDs via WiFi to either of my 4 systems in 4 different rooms. I set this up over 11 years ago initially using a MacBook Pro and currently using a Mac Mini running headless. I purchased a used Mac Mini for $300 about 3 years ago and after initial setup (which took a little over an hour) I haven’t touched it except when I add a new ripped CD. Absolutely no fuss and very reliable. My wife loves it because it is so easy to use. One of the 4 systems is actually her system. We use our iPhones or iPads as remotes to access and select our music files.
Regarding streaming, I don’t use any internet music services but I did do free trials with Amazon, Qobuz, Tidal and Apple. What I do is stream my lossless ripped CDs via WiFi to either of my 4 systems in 4 different rooms. I set this up over 11 years ago initially using a MacBook Pro and currently using a Mac Mini running headless. I purchased a used Mac Mini for $300 about 3 years ago and after initial setup (which took a little over an hour) I haven’t touched it except when I add a new ripped CD. Absolutely no fuss and very reliable. My wife loves it because it is so easy to use. One of the 4 systems is actually her system. We use our iPhones or iPads as remotes to access and select our music files.