Stuart,
So in order to take advantage of one of the music streaming services, and there are several of them, you need a way to get the music streaming to your integrated amplifier. One way is to have a computer hooked up to a DAC, and connect that to the amplifier. The newer way, which is less complicated than using an entire computer, is to use what they are calling a streamer. A streamer is a small component that connects to your internet at home and to the amplifier or preamplifier. It then connects to your online account with the source of the streaming music (I use Tidal HiFi, but there are others).
The "Node 2" is a model name of one of these streamers from a company called Bluesound. There are others on the market as well, from fancy companies like Naim for thousands of dollars, and newer companies such as Auralic, which has entry level all the way on up.
I like the idea of the Bluesound Node 2. It seems easy to use. You can connect it to an external DAC or use the onboard DAC. It is reasonably priced. You control the thing with a smart phone or a tablet.
So for $500 you get a very interesting product that connects you to 4 million full cd quality albums on Tidal HiFi. It may be a little leap of faith if you are not up to speed on the latest digital stuff, but talk about making a change in your system!
Too often we are always talking about squeezing an extra droplet of performance from our already good sounding systems, and often for big money. A move like this gets you nearly all of the music you could ever want. Imagine going to a huge CD store and think, ah yes, I already have 90% of these CDs!
Precisely since you are not fully into all of the contemporary digital developments, I highly recommend this to you. Purchase a Bluesound Node 2 from a place like Best Buy or Crutchfiled, a store that will give you a long trial period with a full refund possible. Spend that $500, and let the other $2K sit idle for the moment. Get a trial account for Tidal HiFi (the $15 per month one that gives you fully uncompressed CD quality music). Plug the Node 2 into your amplifier, and connect it to your home internet. Link it to your Tidal HiFI account, grab your smart phone and sit in the sweet spot. Prepare to be amazed.
If you don't like it, send it back, and call it a free learning experience. If you do like it, sit back and play music, and then decide the next move. That next move could be a subwoofer, or whatever. You may like this so much that you rip your CD collection, and play them through the Node as well, selling the CD player and getting a great DAC. Who knows?
I am super curious to see what you do. Even if you upgrade the amp, I think this is a great experiment to try...