What am I missing streaming music with a Node 2i

Another option to the Lumin D2 is the Teac Reference NT-505 though in addition to streaming like the Lumin it also has the ability to serve as a full function DAC.  I have owned both and prefer the AKM 4497's in the Teac over the Wolfson chipset in the Lumin.  Both use the Lumin app for a control app.  

The Teac NT-505 looks really appealing because of the ability to hook it up directly to the amp. There is also a lot of options for hooking up different digital sources, a NAS and flash drives + headphones. My tube amp uses RCA's and the Teac uses XLR connections. I'm going to ask a possibly stupid question, can I have them both hooked up to the amp at the same time and turn on the one I want, the tube pre will be relegated to phono duty only after I sell the Node 2i.

Not sure I understand what you're asking.  The Teac has both SE and Balanced analog outputs but I don't know if you can hook up both at the same time.  If you are using your Marantz as a control center including bass management how are you going to do those things.  Tell me exactly what you are proposing including the specific gear included.  I have mine connected via balanced IC's to my BHK preamp with the volume on the Teac at unity gain.

The Marantz SR 5012 is for surround sound with tv only. I have a Odyssey Stratos stereo amp and Odyssey Candela tube preamp for 2 channel listening. The Candela has a HT bypass so I can use the mains for the fronts in the surround setup. I am running the Node through the Candela as well. What I'm proposing is using the SE inputs for the Candela and the Balanced for the NT-505 on the same amp. It doesn't sound right to me but I don't want to run the NT-505 through the Candela.