What can I do between the wall and my streamer/DAC?

Another option is putting a network switch after the 45' run of ethernet cable, run by a linear power supply.

Some form of LAN Isolator to the Lumin with a good ethernet cable from the switch. An Eno would suit, or the likes of a Pink Faun.

Much of the responsibility of sound quality rests on your streamer. So, you can fiddle with your routers and cables or concentrate on a great streamer. For me, I use wall wart wifi extenders and great streamers (Aurender N100 and W20SE) and get sound quality equivalent to my amazing analog rig.

I use a TP Link Ethernet over AC adapter.   It works great.   I used to have one made by Netgear and it was noisy.   The TP Link works great.    Unfortunately I can't run hard wire from my router so it's the only way for me

I needed a switch so I bought a TP Link TL-SG2210P  10 port switch with 2 SFP slots

Each slot has a SFP fiber optic module .   I use the TP Link MC220L  fiber optic media converter connected via LC fiber optic cable to the switch.    

One SFP module goes to my Vault 2i and ths other goes to my Aurender N200

TV , computer , and Blu Ray are connected via rg45

Total was around $250 for everything 

Works great  

With a run that long you would benefit from fiber and a good Ethernet cable on the streamer end. I recently replaced my 30 foot Cat 6 with fiber and Cat 8 cable, it was a significant upgrade in sound. And cheap to try, around $120 on Amazon. There is a discussion in this forum with links to gear, worth a try. 

@backwash

If you’re not getting any dropouts, there’s no need to buy anything.

As long as the DAC is getting the data intact (whether wired or wireless), there’s no improvement to be made. This is the beauty of digital data.