Ethernet

In your home, most affordable switches and ports support 1GigE, as do cable modems and routers.  That's not to say the Internet provider will offer you that much bandwidth.  That's Cat 5e.  It's also probably 2x or more what you get from outside.  100 Mbit/s was also something like 10x more than what 96k/24 bit audio required. 

So, it's all overkill.  However, it's best to know your equipment's rated throughput, as bad/slow cables can cause your gear to keep switching speeds and/or disconnect.  So if your gear is 1GigE stick to 5e or better.  Use Cat 6 if your switches/ports support 10GigE.  Again, massive overkill for audio/video.

Check Zoerax cat8 5th gen on Aliexpress. Top quality at a good price

AVANTI AUDIO

https://avantiaudio.com/collections/all-cables/digital-cables

I bought a long 6m run of these . I compared them to the very top end AUDIQUEST DIAMOND and these AA VIVACE Ethernet cable models are true contenders and no pretenders at about half the price or less.

They have ads on AGON. You can order custom lengths .

eg https://www.audiogon.com/listings/lisb4f2j-avanti-audio-vivace-interconnects-cat7-3-0m-ethernet-cable-digital

highly recommended.

STEREO TIMES review

“…. Finally, I added the Vivace CAT-7 Ethernet cable and did some listening via my iTunes library through the JRiver Media Center. For all the improvements that the Vivace cables made in my system, this was probably the biggest.

Until now, most of my listening to computer downloads were with cheap CAT-5 cables or even via WiFi, which is not optimal. But inserting these cables was a game-changer. I’ve spent a lot of the earlier part of this year listening to many musicians under the ACT label. ACT is a progressive European jazz label that features fantastic artists such as pianist Leszek Mozdzer, trombonist Nils Landgren and bassist Lars Danielsson. A recording by Danielsson allowed me to appreciate what this Ethernet cable did for my system. Liberetto is a recording that features pianist Tigran (yes, a one-name performer), percussionist Magnus Ostrom, guitarist John Parricelli, trumpeter Arve Henriksen, and of course Danielsson.

That’s a lot of musicians and a lot of music. They’ve always sounded glorious together, but through the Vivace cables and the Ethernet cable, in particular, the sound was more of an experience. The soundstage blossomed, and the musicians were rendered so finely that it sounded as though the listener occupied the same space. And oh, the way the low-end detail took the sound from being boomy and annoying to rhythmic and natural was something that must be heard to be enjoyed. This cable will not be leaving my system….”

Agree with many here that Blue Jeans would be more than fine for setting a baseline to start.

I'd then start trying different eth cables from the splitter to your streamer and vault.

I have a similar setup today:

Router > Switch > Streamer

I had all blue jeans, but now I only use blue jeans of about 12 feet from Router to Switch (LHY SW-6), and then a 1.5m Sablon eth cable to the streamer.  In my system, it's an upgrade in SQ.

The Avanti cable recommended by akg above looks compelling.  Give it a try.

Can you provide more details on what the "splitter" is?  Is it a switch or hub, or something else?

Blue Jeans is what you want. Anything over is a scam. Ask yourself - does Amazon (Tidal, etc) use $1000 Ethernet cables in their data centers? No? Why would you?