Alex, I will use the forum to ask a few questions - I hope they can be of use to others.
Excellent, let me see if I can help!
Can we protect the Statement installation with a password? It seems anyone using my,unnuos.com can change the configuration or access the files in the SDD from a windows machine connected to the network.
The whole "my.innuos.com" thing is an ingenious way to locate your device, *from another device on your local network*. What does that mean? That it'll only work if whoever's accessing it already has access to your local network.
Want to give it a try? On your mobile, while connected to your local network (via Wi-Fi), "my.innuos.com" will work just fine. Now, disable Wi-Fi, and just use your phone's data network. That way you will NOT be on your local network anymore. Then try "my.innuos.com" again. Your Statement won't be visible anymore, even though it's still there, operational, maybe even playing music. It's just that your phone is not on your local network anymore, and so the Innuos is off-limits to it.
As it is, there is no access control built into the Innuos software, and that's for simplicity' sake. That's part of what makes it easy to set up and use (one less password).
What is the best sounding configuration for Roon of the three possible ones?
What do you mean here? Roon has a myriad of options and configurations. The first thing I'd do is disable all sorts of DSP within Roon, by going into Settings > Audio > <locate your dCS here> > gears > DSP Engine.
Does a file being played from the internal SDD sound better than played from a NAS?
If I ever did that comparison, it was very early on, and I don't remember either way, so possibly it was not significant. I will have to give that one a try now...
You referred that a WAV file sounds better than a FLAC. What should we do with HiRez PCM files?
If you've already purchased them in FLAC, go ahead and convert them using an app on your Mac or PC, like dBpowerAmp or XLD, then store the AIFF files (preferable to WAV) and ditch the FLAC.
If you're buying new albums, I recommend you purchase either WAV or AIFF files, not FLAC.
And, as I said, when ripping, go with the WAV option with the Innuos software.
Hope this helps!