I went to system info and I have no section listed for power at all. System Info lists many sections for CPU, memory, devices, OS, etc etc but nothing at all about power. This is true if I connect through gizmo, or play locally on the HTPC (the two conditions which keep the htpc awake)
On the PC clients, I do have "play local file if one that matches library server file is found" but I do not have the files stored on the disk of either Client PC. The PC on LAN however would likely have access to the same file paths as the server, so I will try to see if this setting has any issue. However that still makes very little sense to me, because if the Client PC is pulling the source file directly from the NAS on network, why would it disconnect/stop playing when the HTPC sleeps? Either way, I'll test tonight and see how it works out.
Second, I would think that the Remote Client PC would have no such access to the NAS and should not trigger that issue either.
And lastly, there appears to be a clear difference in the Wake on LAN behavior between PC clients and Gizmo, because neither PC client appears to be able to wake the HTPC from sleep, but the Gizmo can. Is there an explicit WoL setting I have to enable in the PC clients?