Looking at the specification for the Audio Engine 2+ desktop speakers they have a USB audio input… thus you should be able to connect them directly to the Nucleus via a USB cable.
If distance is an issue then I suggest adding a Roon Ready streamer or if your ok with a little DIY a Raspberry Pi setup to run Roon Bridge.
The Nucleus is upstairs with an Ethernet outlet downstairs. It appears as though I could connect a Wiim ProPlus to the Ethernet with its analog output to the AudioEngine 2+ via RCA. IIRC the Nucleus doesn’t output WiFi.
You can use ethernet or WiFi to connect a streamer. The fact that the Nucleus itself does not have WiFi is irrelevant because your router (to which the Nucleus is connected by ethernet) does have WiFi.
The wiim pro plus would certainly work (WiFi or wired ethernet) connecting to the Audio engine by it’s analogue outputs.
However, you could also consider a bridge device like the Fiio SR11 which would connect to the Audio engine by USB. The SR11 costs half of what the Wiim Pro Plus does in the UK.
I think the Audio Engine 2+ can take WiFi input, so the connection might be seamless. I use an M2 Mac Mini or iPad to control Roon. I’ll fire up the AE 2+ and see if Roon finds it. I wonder if I could use USB C from the M2 Mini to the AE 2+ for Roon.
Yes that would work, provided you had a Roon installed on the Mac Mini.
Other than a cable it’s a no cost solution, as the Mac Mini would effectively be the RAAT streaming system which would identify itself to the Nucleus as an audio zone.
I’d certainly trial it before spending on a network to USB streaming device.
From what I can tell the A2+ do not have WiFi, they only have Bluetooth, USB (aptX), and analog (RCA/3.5mm) inputs.
Like @Carl said you could connect vis USB directly to the Nucleus or like you said to your Wiim ProPlus vis analog. If the Wiim ProPlus can connect to the WiFi AP on your router you would not need the ethernet, however, ethernet would be more reliable/stable than WiFi.
As an alternative, you could buy one of the WiFi adapters Audioengine makes:
I use the M2 Mini with a 27" Studio display as my primary computer. Roon is installed and sees the Nucleus, KEF LS60, and Sony HT A9. I’ll connect the AE 2+ to the Mini via USB.