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?