Which combination of components (Streamer, DAC, Preamp, Amp, etc.) are most future-proof?

Sure thing 

@hilde45

 I was also concerned about the AUDIOLAB 6000N had no display at first.  But even if it did i would more than likely have to get out of my chair and go have a look at the display. Now where did I put my glasses??  I would use my smart phone or ipad to control and stream hi rez music 99% of the time anyway. With the DTS Play-fi interface they make it pretty easy to use and they are updating with new features all the time.
Of coarse I'm taking a chance buying it sight on seen, but my thinking is, it's not that much money and that allows me to spend more money on a good external DAC that should not become redundant.  For what ever reason the Audiolab 6000N becomes redundant in a few years it ( I would be surprized) I'll just purchase a more up to date streamer. Hey whatever you decide I'm sure you can't go wrong as there are so many great products to choose from.  Good luck and the hunt is most of the fun!

“Software is stable and mature. Most systems are run off of Linux or Windows which are not going anywhere”.

I agree with @david_ten. I have been using Linux based streamer from Aurender for last 5 plus years. It’s easily one of the best investment I’ve made...they have kept their products relevant since their inception with consistent software updates and excellent customer support.

The choice of components typically driven by budget and your goals. Are you in for long haul or short haul? Short haul, node 2i will do just fine but if you’re in for long haul, explore quality driven offerings from Aurender, Lumin and Innuos.

As far as answering your question about future proofing - You could go on building your system one component at a time i.e separates that affords you the most flexibility or consider something like a DCS Bartok.

All Simaudio products are upgrade-able for both hardware and firmware and they have a 2 year buy back program for complete upgrades. 

@soma70 Thanks for the advice; I had moved away from separate toward integrated, though now I’m surfing the web about some separates by PS Audio and the preamp includes the DAC, so maybe I’m back in your direction. I wonder which tube-preamp/DAC/streamer you like?

@jrwaudio — I hear you about "where are my glasses"! I am officially middle-aged, applying low-vision standards to my components! That said, I’ve got to just say it out loud: I like a volume knob, balance knob and even (gasp) a bass and treble knob. But they’re not dealbreakers.

@lalitk — agree about Linux. Regarding your question about short/long haul, I suppose the answer is this: lack of a large listening room to build out a system is causing me to rebuild/revise my present system in a modest way — with smaller speakers. A basement remodel is on the longer horizon, but in the meantime, I purchased good small speakers for my office and am now researching better source, power, etc. If and when I can transition to a larger listening space, I’ll have good source and power, and then may swap out speakers. I'll look harder at room acoustics and other issues (cables, etc.).
   The immediate challenge for me is to go step-wise. I just spent $2500 on new speakers and sub, and so I don’t want to spend a crazy amount on streamers before I figure out what good power might cost and which power matches best with my new speakers (they're getting built). I want to spend what’s proportionate on the other components, given the speakers. (I know this leads to a contentious topic, but personally, I’m comfortable spending about the same on source/DAC as speakers and on amplification as speakers, but not wildly more on any other main element of the system.) For these reasons, I’m not entertaining streamers that cost as much as what good power might.

Budget-wise, I suppose this works out (estimating *as if* they were separates):
$2500 on mains/sub (spent)
~ $1500 preamp (researching now)
~ $1500 amp (researching now)
~ $800 DAC (researching now)
~ ?? Streamer (researching now)

@skypunk I’ll look into Simaudio. Thank you!