@soix Yes and yes are the short answers.
As you likely know, iFi has 3 levels of power supplies, and it shipped the first level with the Zen Stream. I had an extra iFi iPowerX lying around, so I used that for a while with the ZS. Then I got the itch to try their highest tier of power supply, which I'm currently using. Their highest PSU gave a little extra refinement to the sound.
I haven't tried the ZS with the wifi antennas. I went hardwired out of the gate.
Farther upstream, I recently upgraded the home network to multi-gig LAN and WAN. Because no audiophile companies have a multi-gig switches out yet, I'm using a TP-Link multi-gig switch directly into the ZS. I wanted to get used to the sound before I reinstalled the optical converters to see if there was any difference converting the network from ethernet to optical right before entering the ZS. Speaking of iFi and optical, have you seen iFi's latest streamer?--the iFi Neo Stream? It comes with a low noise optical converter and optical cable to connect to the optical input on the Neo Stream. I'm interested, but I'm uncertain whether it would be an upgrade for me.