Bluesound Node 2i , Azur 851n or ...

I’m building a streaming system to compliment my Ascend Sierra 2 speakers and Odyssey Kismet in Khartago amplifier. 

Bluesound Node 2i ? Used Cambridge Azur 851n ? Used Sony Hap-z1es ? Others?

 I would like to control the system using an iPhone or iPad and don’t want to use a computer. 

I’m looking most especially for ultimate SQ (MQA? DSD? Etc.) via Tidal, Deezer and Apple Music and/or hard drive (but not having to use a separate computer). 

I think that I may eventually add an external dac such as PS Audio Stellar Gain Cell DAC etc. 

I will also probably eventually add a tube preamp such as Odyssey Candela etc. and probably also (rather soon) add a subwoofer by Rythmik etc. 

Would a connection via AirPlay 2 and Ethernet be my best option and if so, is there a easy way to use a second router and / or modem so that I don’t have to run a twenty foot run of Ethernet chord? 

Finally, I have listed similar posts in the past but still don’t know exactly which way to go regarding this , so , please no roasting me! Ha 

If you are going to use AirPlay, or BT, why would you need Ethernet?
The streaming services that you listed aren’t the highest quality sound.  For that check out Tidal or Qobuz.
  The Bluesound Node 2i should meet all your needs.
I suspect the 851N sounds better than the Bluesound. I have a Vault 2 running it through the DAC in my 851C and it sounds better than the DAC in the Bluesound. It’s night and day. I bought the Vault for ripping and I very much enjoy it. The DAC in the Cambridge is fairly good and think it will satisfy most with Tidal HiFi. 
I've owned the Node 2 for 3 years and treated it to really good cables (i.e. power and IC's) and it performs extremely well - so well in fact, that I have stopped looking for ways to improve on it - perhaps I'm not a true audiophile?

I use the Ethernet port because my Wifi setup (i.e. the router) has a problem with 24/196 files

I was so impressed I also bought the Powernode 2 and the Pulse Mini.

Regards - Steve 
I have had the Node 2i for a couple weeks. Mainly for Tidal MQA. It sounds very good with good cabling and a good system. Performs best in my main system, but also sounds very good in my secondary system. BlueOS navigates well and it also sounds great through my DAC, when running Tidal MQA and non MQA. The internet radio stations are fun to have immediate access to and a number of them sound very good. I think it’s a great bargain at 500.00.
I have been using Bluesound gear since 2014, have a Node 2i in my main rig, and a couple of first generation Bluesound Nodes and a Powernode in use elsewhere in my household.  

What I like about the node is its ease of use combined with its flexibility.  I think that the BluOS interface is the next best thing to Roon (and far more affordable), but if Roon is what you are after now or in the future, the Bluesound gear are Roon ready.   Android, Ipad, PC, Mac, all can interface with BluOS.

As to whether to go wired or wireless, all things being equal go wired.  My experience is that a wired connection makes for a much better experience, especially when it comes to streaming Tidal.

One relatively easy way to support a wired connection, and one that I use in my house is the employment of powerline ethernet devices (I use Netgear).   

The Bluesound internal DAC is decent, and certainly listenable, but if you really want to kick things up a notch (or much more, the sky really is the limit), then down the road think about investing in an outboard DAC, which you can connect to via either Toslink or Coax.  I utilize an outboard DAC in my main rig.  Beginning in 2014 I was using a Bryston BDA-1, and more recently upgraded to a Chord Qutest.   Again what I most like about the Bluesound kit is its flexibility.
Re MQA, I'd look at it as icing on the cake, and not the main event.
One of the nice things about the Bluesound gear is that when used with an outboard DAC, the Bluesound device will handle the first MQA unfold.  This gets you as far as 96K.  With a capable outboard DAC such as the Bryston or Chord, there is no comparison.   Music via a DAC of this ilk, in my opinion, with or without MQA will get you much greater SQ.   But then this should be expected given the differential in price point.  But all the same, the Bluesound will get you in the ball game, is  very listenable on its own, and provides a path forward should you desire to take it.

Good luck with whatever you decide.

Mahler123 - I’m basing the Airplay 2 with Ethernet (Airplay 2 from iPhone to Muso which is connected to router with Ethernet) off of how I currently use my Naim Muso. I was really skeptical upon the advice of Naim regarding this but it really does give the best SQ by far at least with the Muso. Perhaps the superiority of that setup is just Unique to the Muso? 
It looks as if I have several options on used / open box units available other than the Node 2i that are not too terribly more expensive probably around 800.00 to 1100. Although I’m all about spending less money, in the big scheme of things it’s not all that much more if it would add considerable utility and SQ. 

One big question I have is how (or how not) an external hard drive connection would work with the Node 2i etc and also,  what really is the advantage of adding one anyway?
 It appears as if , for instance, the Azur 851n allows and external hard drive to be easily added by just plugging into it. Again though, what exactly is the advantage to this especially from a SQ angle? DSD? How would (or would not) later adding a better DAC affect this? Finally, how would a tube (or SS)  preamp affect things? 

Can an anyone please help me sort these things out? 

Thanks again! 
You can connect an external hard drive to the a/o input on the back of the node2i which then allows you to access the hard drive through the BluOS app, via an iPad etc. The cables and adapters are included in the Node box. The tracks then play through the node 2i and it’s own DAC or you can bypass the DAC to a outboard DAC. Lots of options. However you should talk with a Bluesound rep to assure compatibility on how you wish to access the various sources of data. I have read reviews where some had trouble with initial setups. I did not have any of the issues they note. There also is a Bluesound Node 2i forum that you can refer to for other questions you may have, it’s a good read on the product usage and capabilities. I really like mine and it sounds great on its own and with my Schiit Yggdrasil DAC.