Do I need a stand alone streamer?

A Wiims Mini into the Toslink input on the Marantz will do

I’m hoping you’re streaming either over Wi-Fi or a direct Ethernet connection from your router rather than Bluetooth?  Anyway, it’s very possible something like a Node or Wiim will be better streamers than the one in your AVR, but whether they’d be a meaningful upgrade in the context of your system is an unknown so if I’m you I’d get one that’s returnable (Crutchfield, etc.) in case the improvements aren’t all that.  If 2-channel is important to you it’s certainly worth trying because streamers can make a difference.  Looks like you’d want to use an SPDIF digital cable and you want something at least decent because they do matter (I wouldn’t use optical because it’s limited to 24/96 resolution and involves extra conversions to optical and back).  Here’s one option that’s pretty decent and won’t break the bank (you want at least 1 meter length)…

https://sites.google.com/view/pine-tree-audio/interconnects/single-ended/nexus

If the streamer has an onboard DAC you could just use regular interconnects to your AVR and compare that to the DAC in the AVR to see which sounds better.  Hope this helps, and best of luck.

I was using a Bluetooth receiver with LDAC (Mii Audio) and switching to the Bluesound NODE N130 was a noticeable improvement for 3 reasons: 

1) Ability to stream FLAC (using Tidal) files directly from my wifi.

2) No more pesky interruptions from my phone notifications during listening.

3) the Node DAC is excellent and I do not need an outboard DAC.

Thanks. I am sold on the Bluesound Node N130. But I am am also looking at Cambridge MXN10 as an alternate. Price is a factor. 

@manhattan1  -  Both are good choices at this price point.  There is an advantage with the Bluesound N130 due the better BlueOS app.