@cleeds The physical distance between the modem/router and streamer is of little or no consequence. The only possible issue would be if wifi enabled, emi-rfi can contaminate nearby components, since wifi disabled no issue. @foggyus91 explains why quality audiophile equipment would be less impacted by close proximity, still, remember we are disabling wifi which makes the issue moot.
If you're worried about internally generated noise migrating via LAN cables, shorter is always better, longer LAN cable lengths don't magically drain noise away.. Another added bonus of shorter lengths is less financial expenditure.
Bottom line, modems and routers with wifi disabled, sitting in close proximity to any or all other streaming components will not contaminate those components in any way. The benefits were obvious in my setup.
As @jeffbij points out, this setup provides both a 'dirty' and 'clean' home network, all streaming components go on clean side. For a more in depth explanation of a 'clean' or audio home network people should check out the Dejitter IT Switch X, this is a highly modified Mikrotik managed switch, replaces router altogether, I suspect we'll be seeing more of managed switches replacing routers in the future. These noisy routers, even with wifi disabled don't belong in really high end streaming setups.