Interesting hobby this. My thoughts on a couple of recent themes. First I prefer single supply on the ND 555.
I have no experience with Melco but hear the difference with a rip of a CD via the core versus a previously ripped file from the serv or in respect of a file of undetirminable providence. I had noticed this previously with my NDS and frankly it came as a bit of a surprise.
I was intrigued with Darke Bears experience with hard wiring the iPad to Ethernet and tried this last night. I felt their were pros and cons but accept that this could in part be how I configured the connections. I then tried listening with the wi fi on the iPad turned off. Ie select album to play then turn wifi off on the iPad. Again I was surprised at what I heard. Practically though doing that ie turning wi fi on and off as required is a whole lot less hasell than going through the whole registration set up thing when using an Ethernet connection. As they say everything makes a difference but the challenge is in trying to figure out whether it’s better or worse
The ND555 sounds very different over the first several weeks of its life and I'd try the two supplies after it had been run-in for over a month if you had negative results before ruling it out ahead. There was another poster who also said they had preferred a single supply and then only later found that two supplies was a lot better. Two supplies makes the ND555 more revealing of both music and run-in artifacts and the latter can shout at you more unpleasantly. Always personal, but my demo was conclusive that in my system the ND555 was significantly better with two supplies in terms of detail, stability and more extended and better articulated bass and HF - not jut the HiFi sound aspects but I preferred it musically. It is fine with one supply but not worse with two IMO.
The Ripping - I've said all I can at this point and essentially make sure you have that optimal for you and check it out yourself.
On the WiFi use for the control App - I find the noise-floor lower when the WiFi is off and hear an obvious (to me) wall off noise drop from the sound-stage when I turn-off the house WiFi and get better depth info and immersion into the music and it just feels more relaxing to listen to. Why - well removing a wide-band noise transmitter may be part of the answer - perhaps?
However as you also notice the present Naim App has a problem with operating without WiFi and goes into a pointless sulk telling you that you have no WiFi - but still works as you have a wired-LAN but need to re-register. It takes 20 secs to do and I've done it so many times I'm used to it as I refuse to be bullied to conform when I want it otherwise - hopefully the next Beta App when available will sort that out - I shall see.
WiFi is convenient but I find I don't really need it a lot in my house as it is all Ethernet wired so I have LAN points everywhere to use - so I use what gives me best sound. Different systems may sound very different with respect to interactions with RF signals and WiFi - mine is a large cross-section for anything to make ingress at RF frequencies and the noise floor is where I'd first expect I may hear that if present. Plus I was curious as to the effect of removing a local transmitter would have - people assume it is all fine, perhaps it is as it is very convenient, but is there any down-side.