Point of diminishing returns for a Network Streamers?

My only contribution to this discussion is, if you try to connect android to ifi zen streamer, be ready for a mountain of aggravation. My experiment lasted 3 days. Endless attempts of connectivity and android developper settings resulted in a big fat zero signal passing through the zen to my Gustard x26 pro. Luckily I bought the zen from crutch field and, upon request they immediately issued a return label for full refund. Hats off to them. I understand that connecting the zen to iPhone is a much more pleasurable experience. Bottom line, going to all that trouble to connect android to zen is not worth it to me since android to Gustard through bluetooth is a piece of cake and probably not much worse than through the zen since the signal originates from android. My sanity is slowly returning, what a nightmare that was!

Double plus one (1984 reference) on going from a computer to a streamer or sterner/DAC. Been there, Done that. 

Cleaning up the Ethernet chain w/ EtherREGEN and the works also a wow. 

I wonder why you are using an old computer.  My BlueSound Node 2i streams Tidal without using a computer.  When I purchased the BlueSound Node 2i the retailer convinced me to al purchase a Project DAC.  Adding the Project DAC caused the bass too sound thin, so I sold it on Audiogon.  I have heard some expensive DAC and based on that they do sound better.   

+1 for LUMIN streamers.  I too use a Mac, a 2014 vintage MacMini with a 4-core I-7 processor. A few specifics.

The improvement in clarity and the timbre of instruments was very noticeable. I went from (1) a direct USB connection from the MacMini to my DAC to (2) Ethernet from MacMini to a Linksys Ethernet switch, then Ethernet from the switch to the LUMIN, and USB to my DAC.

A second point is that my DAC, pre-amp and the rest of my system are capable of a high level of clarity and resolution. My DAC is an Ayre Acoustics QB-9 with the Twenty upgrade, and I use an Ayre Acoustics K-5xe pre-amp. Both of those units cost between 50% and 75% more than the LUMIN U1 Mini. My Ethernet cables are by Audioquest, but were not overly expensive (about $150 each at the time) and the USB cable from the LUMIN to the Ayre DAC is a Transparent cable. 

While I believe there can be further improvements to my system by going to a dedicated music server vs. the MacMini, and by upgrading my cables and Ethernet, having tried some such tweaks I found the improvements marginal compared to adding the LUMIN streamer. The LUMIN and the Ayre DAC have excellent USB interfaces compared to many if not most comparable products. I think the upgrade that may make the most sense for me is to go to an optical Ethernet system, which I will consider at some point. Optical is inherently less prone to noise than copper wires.

I can also say that to my ears the LUMIN is noticeably superior to the Node 2i, the version I demo'd. I can't speak to the new iFi or Project streamers. As always one's budget has a bearing on the final decision.

Happy listening. 

All a streamer really needs to do is transmit the bits from local storage or a music service to your DAC intact. It sounds as if your setup already does this. There’s no need to make a change unless you’re detecting noise / pops / ticks / dropouts during playback.

As a reference, have a listen to the ’Bad cable’ sound sample from this link - What does a bad USB (or other digital audio) cable sound like? This is also what you'd hear from a streamer with suboptimal digital interfaces.

If you’re focused on improving / changing the sound of your system, you’ll get more bang for your buck if you look at different speakers or headphones than electronics IMHO.