I'm not saying mac mini is at top of servers list, but OP already has one, only needs OS update to get it back to operable state.
Also, I suspect many have underestimated optimized and modded mini as server only. Certainly as a renderer it is sadly out of date, but as server only and modded to optimal state it is quite good. Compared to many other servers, $5k and below, I don't see liabilities, with the right hardware mini is actually superior to this crowd, biggest liability is Mac OS, even with app wipe, still more processes running than needed, even with this I'm only running at 3-5% processor ability, nearly 50% of that used for Roon. While I can't state a comp with other servers in present system, I am getting amazing sound quality from my present streaming setup. I do plan on comparing to extreme high end server soon, this atx motherboard server built to Taiko Extreme level of quality, best of best everything going into this diy build, including choke based power supply.
Based on you guys, I'd stick with Meitner as streamer, so only question is server vs straight out of router. I'd get lps for router in either case.
As for switches, I have extremely unique streaming setup. Modem and router both set up close to my system, Modem>lps router(via AQ Vodka)>mini(via Vodka)>FMC(via Vodka, soon to be OpticalModule instead of generic FMC)>OpticalRendu>dac(via AQ Diamond usb). The switch I tried was RenoLabs Ultimate, OXCO clock and lps built in, this went between router and mini, diminished sound quality, less spaciousness, excessively etched images, smaller sound stage. I surmise this due to mis-matched clocks or excessive clocking. Ed Meitner states clocks should only be installed at closest point to circuit their clocking, this may be evidence of that. I also recently tried FMC (both powered by lps) and all ethernet AQ Vodka in same position as switch, while better than switch, still no cigar, again less spacious vs router only, pretty equivalent on sound stage, imaging front. Next try will be Network Acoustics Muon filter in same position. In my setup, router direct to server best, on paper this should not be case, router vs switch or FMC noisier.
Also points to possibility Meitner MA3 may perform best direct connection to router, especially if powered by lps. I think OP should try this configuration first, then compare to other setups.