How to build a super simple streaming system

Your missing a part, it is called an amplifier!  The BlueSound is an endpoint for streaming but the output is line level, not speaker level.  Some amplifiers have knobs for volume, which would be analog control.  The BS Node controls volume digitally and you have an app on your phone for that, too.  But, to be honest, the analog volume is the way to go for best sound quality.  If you want an analog remote look at this little gem: https://www.schiit.com/products/saga-s

It has switched inputs, buffered, and a neat analog volume control, all of which is remote controlled.  It does not produce gain, so the output is equal to the input.

So the bottom line is add an amplifier to suit the speakers and control it via your phone or get the Schiit unit and use analog volume control with remote.

The Genelecs are powered speakers, you do NOT need an amplifier, just a cable.

Spotify is fun but always poor sound quality regardless of system. Though some like it 

OP might consider Roon ready KEF LS0 Wireless II or LS60.  Only external requirement is a modem/router.  Connection can be Ethernet or WiFi.  Sound quality can be excellent, and the KEF app makes set up easy and is a delight to use.  eARC provides uncompressed TV sound; coax provides 192/24 access to digital sources like a disc player,

To use the Node with the genelecs all you need is to run an interconnect cable from the RCA connections to the Genelecs and use the bluesound app on your phone to control the volume:

Yes if you don't want to buy anything else you can connect the analog outputs of the Node to the G3's and use the Blusound app to control the volume but that is compromising sound quality. I would buy something like the Saga or another passive preamp with a remote to control the volume.  The you would set the volume on the Node to maximum and use the preamp for volume control.  Saga is not the only option in that arena though.

I would spend a couple hundred for a better DAC with a volume control.

@fuzztone +1! Then add a subscription to Qobuz or Tidal.

@fuzztone Do you mean get a different streamer/DAC instead of the Bluesound or get a better DAC than is what’s on board the Bluesound? What brands should I be looking at? Thanks very much!

Start with the Bluesound and the G3. Connect with a simple RCA interconnect. Control the volume with the Bluesound BluOS app on an iPad or IPhone (assuming you have one or both). I suggest Radio Paradise MQA internet radio station for free to try out streaming with good quality files. You can subscribe to Tidal or Qobuz at leisure at any time. I think you’ll be happy with that. You can always add other items later.

@snbeall, +1.  If you decide you want a better way to control volume, a S.M.S.L DAC such as the DO100 between the Node and Genelecs will provide better sound and remote control.