Do I need a stand alone streamer?

What’s the rest of the equipment in your system?

Besides the Marantz I have two Wharfedale EVO4.4 tower speakers, two vintage B&W Matrix speakers, a Canton center channel speaker and an SVS subwoofer. 

Unless I’m mistaken, you were using some form of Bluetooth to get music through that unit. So if I’m correct in that statement, then a standalone streamer, even this WIIM mini https://www.wiimhome.com/wiimmini/overview would be an improvement over what you’re listening to now. 
there are other options out there like blue sound nodes, that would probably sound better But nothing in that price range will come close to the sound quality you can get when you step up into a Innuos https://innuos.com/pulse-mini/.  
so I guess what I’m saying is get your toes wet, and then save enough nickels until you can do a dive in the deep end. No sense in wasting your time in the shallow end. 

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.

The CA is definitely a step up from the Node.  I also prefer the CA app.

I’m leaning to the Cambridge MXN10, but it seems to be out of stock everywhere. 

I found an AXN10, which is the same streamer in a larger chassis, available from LISTEN UP, though on back order. I placed an order with probable shipment later this month. Now the question is, what is the best connection to my AVR?  Should I go with the RCA connection or digital coax?

I would try both ways and see which of the built in DACs you like better.

And keep an eye on your order.  Cambridge Audio has been selling the AXN10 and MXN10 for $399 for the last 6 months (?) and now everyone is on back order ???  They maybe getting ready to release something new as a replacement for both units.

Wiim Ultra should be auditioned. Excellent software, works great with Qobuz Connect.