Do different streamers really sound different when using an external DAC

Unfortunately, all the variables mentioned do have an impact. IMHE, an improved streamer will make a bigger difference than just adding ethernet vs. wifi. One important part of that change is that most users of betters streamers will be more likely to use a high quality linear power supply on the streamer. Don't underestimate the value of the LPS!  

If wiring ethernet through your house isn't an option, powerline adapters that use the copper already routing electrical are a good interim option. Here's an example of the current model of one I used successfully. https://www.amazon.com/TP-Link-AV600-Powerline-Ethernet-Adapter/dp/B00AWRUICG?th=1

Mesh is simply a better WIFI methodology. It still sends wifi through the air and noise degradation is still an issue. I have Eero mesh wifi and it sounds nowhere near as good as wired ethernet (between router, Synology NAS and Sonicorbiter in one room and audio rig including ethernet to opticalRendu in the other room). 

I would sum up this thread in order of priority as:

1. upgrade the streamer including LPS. Lean towards something compatible with Roon, Squeezebox or OpenHome DLNA/UPnP apps to limit reliance on a small development team.
2. use ethernet if possible, powerline adapter otherwise, any wifi as last option.

While the Teac mentioned may be a great choice, I'd think of it similar to integrated amps vs. separate amp/pre. IMHO, I'd prefer separates in anticipation of future DAC upgrades, based on the frequent progress in DACs. YMMV. Cheers,

Spencer

@sbank That's a cool gadget for sure but how could that sound better than wifi?  Only asking because I use a mesh setup too and hardwire from the base of one of the mesh units but I cant see how using something where the signal is going thru actual electrical current could be cleaner than a wireless wifi signal.  

If so then I'm all in on one of those units but I just can't see how that could be a cleaner signal, wouldn't there be noise introduced that way even more so?

@blkwrxwgn I can’t explain it, and would say with Amazon, it can’t hurt to try and see. The same same concern crossed my mind. Maybe airborne  RFI, EMI, etc are more detrimental than the noise they the copper electrical? A few on audiophilestyle reported good results, so I tried it until running ethernet was an option for me. If someone explains why it wouldn’t make sense, that’s fine. Cheers,

Spencer

Just about ready to order one of these powerline adapters on Amazon to try hooking up via ethernet. In the description it states that both the "send" and "receive" units need to be on the same circuit. Since my modem is upstairs which is a different circuit (on my circuit breaker), than my audio system, which is one floor below, will this no longer work?

Bluesound is great with a wired either net connection,  good external DAC and decent cables. I could not say one is better than the other compared to the U1.

Sounds maybe a bit different but not better.