Noob question about streaming . . .

You have a long journey to get good sound ,for 1 the junk $5 power supply to your router needs to be replaced by a linear power supply ,little green computer  sells them $300 , then you need a decent Ethernet switch ,LTY SW8

2 decent Ethernet cables the end point cable is more important 

Pangea dual wire $50 each is good enough for yours . These are bare minimum 

to get better sound. I would though save for the Denafrips Aries which is just under $1k which is night and day better then your current built in dac.

Whichever streaming service you go with, tidal or qobuz, I’d still look at adding Roon. 

I have the AV7704 and it’s a solid HT preamp. I would definitely try the Wiim Pro and Tidal to determine whether it’s worth the difference. Personally, I typically utilize Spotify Connect from either my iPad or phone with this preamp and it sounds pretty good. I also appreciate the convenience of staying within Spotify and simply “Spotify connecting” to the Marantz without having to switch any inputs. Convenience and simplicity override ultimate fidelity in my situation. 

I’m still waiting for Tidal Connect, but don’t think this is in the future anytime soon. For clarification are you going through HEOS to access Tidal or are you staying within the Tidal app and AirPlay to the Marantz? Apologies in advance if I missed that.

I don’t think you should pay for another DAC, but I do think it’s worth it to have direct streaming of Qobuz or Tidal that doesn’t involve a tablet or phone as an intermediary. I have Roon and while it’s OK, I find the overhead of keeping another server, and paying for it as yet another subscription kind of burdensome. If I didn’t have so much music on disk I’d probably give it up for something simpler.

IMHO, you want a little box with Ethernet on one side, and S/PDIF on the other.  You could get a combined streamer/DAC, which would improve the digital resolution you can download also.

Here is one example, so I’d say don’t spend more than the ifi Zen streamer.

You should be able to stream Tidal through HEOS in your Marantz. I have no direct experience with HEOS, but most reviews I've seen consider it inferior to the Wiim or Bluesound software. Try it, and if it works fine with your Tidal subscription, then leave it be. Note that Tidal also has Tidal Connect which allows you to use their app as a controller, which is usually preferred by many users over their streamer's software. I don't believe that HEOS supports Tidal Connect.

The advantage of the Wiim streamer over HEOS would be a better software suite and the ability to use Tidal Connect.