Where/how to start?

The standard "starter" answer is get a Bluesound Node and Tidal Subscription $~600). I prefer Qobuz but note sure if Node supports that. Node got all you need to come out of the gate for your first experience. Just run RCA into one of your Pre or use one of the Optical in on the Oppo, DAC proly better in that unit than the Node. Stream with that while you acclimate to the digital landscape. 

Got wired ethernet at your 2 channel set up or Wifi?

I agree , get a Node .   Its great for the money.  If you have a large CD collection maybe look at the Bluesound Vault 2i and you can easily archive all of your CDs.  Put a CD in and it rips it to an internal HD.   I love mine, it and the Node can be controlled from your phone. PC , Tablet.   Easy to use .   

You definitely want to ditch the Bluetooth and use a service like Qobuz.   

Thanks.

It appears that Bluesound Node (N130?) + Tidal subscription using OPPO’s DAC is one of the best (simplest and cheapest) options. Once I get used to the streaming music, I’ll think about upgrading to a more high end streamer.

[edit] I came across Cambridge Audio CXN V2. Would it be better in sound than Bluesound Node? Having a display feature seems to be very convenient.

My Ethernet router is far away from my components. Then, I can use a wall wart WiFi extender?

I am not sure about the Node model number.  Its the basic unit with no disk storage.  I am purdy sure the Node is Wifi capable so you can start with just setting up the node on you existing network.   If that is flakey and you are getting drops then you can augment your network.  Many people on this forum have success with extenders and wal warts but I personally think that technology sucks.  At least it has for me and people I know.   I would suggest exploring going to a mesh network topology.  Little extra $$ but worth it if you are going to stream, easy setup as well. Have one of the network-nodes at your rig and hardwire ethernet to the Blue Sound-Node. 

The Cambridge unit is also nice but its double the $$.   But also a good choice. 

Test the waters with the Node.  If streaming is for you (hooked on the crack pipe)  then you can start to explore whether you want separates or all in one streamer/DAC from high end manufactures like Bryston, Lumin and Moon.

Another option for 'testing the waters' on a budget using the DAC in your Oppo is the iFi Zen stream. $400. A streamer only, no internal DAC.