Point of higher priced streamer?

You should keep pursuing this on your ASR thread. Streamers have one function take the TCP/IP stack and convert it to USB or SPDIF or whatever you connect to your DAC with. The OS handles this function and if it doesn't get it right the DAC won't know what it's getting so this process has to be fairly universal considering all the streamer/ DAC combinations. There could be variations in the amount of distortion or noise that is passed to the DAC but any modern well designed DAC will be able to handle it. You mention all the expensive items your accociates have in their systems but you haven't mentioned one of the most important in the entire chain, what modem do they use? Odds are it's a basic $100-$200 modem required to work with their ISP. If this $100 box is good enough to make your digital stream from the analog input from the wire outside why worry about the router or streamer passing it on. Same deal here in the US everyone talks about enormous SQ improvement with every cable, box and fuse they toss in but combined none of it not one single component, unless it's really freaking bad will be audible above the amount of distortion in speakers. It took me more years and money wasted than I care to admit to realize that one simple truth. If you have the money and want the bling go for it. 

@sangbro For the purpose of playing music via airplay from an iPad to a DAC you don’t need a streamer. Just get a used airport express with digital optical output into your DAC and then you select this airport express as your speaker.
Sound will be good.
If you get a streamer like Bluesound configure the iPad such that it serves merely as remote control, I.e. signal path is from your Wi-Fi to Bluesound to DAC, iPad is not in the path. This solution is very good. If Wi-Fi is good (eg, Google or Linksys mesh), connecting Bluesound via Wi-Fi is superior to Ethernet, I.m.e.
Even better: Get Roon. I run a roon core on a dedicated MacBook via WiFi to a couple OPPO 205 - I have yet to find better (and I have been looking quite a bit).

Since we're talking about digital data, shouldn't it be easy to prove there is a difference? Couldn't you checksum packages and compare the same content from two sources?

Hey @sangbro, you provided a totally different prospective now, thanks for sharing. It seems like you are starting from scratch, but with a sizable budget for starters. I’d say figure out the big items first. Like speakers, amp, DAC. Get a modest streamer just to get you started, like Node 2i, or a microRendu and such, then upgrade down the road if you still have the desire and satisfaction.

+1, @thyname, follow the solid advise and you won’t be sorry.
A streamer wired with a quality RJ45 cable (like Supra CAT8) will sound better than WiFi or Bluetooth connection.