late to streaming, recommendations?

Since you selected the lumin u2 streamer and suggested that at some point you'll be ready to upgrade your DAC, you may want to understand which output through which the lumin delivers its best for performance. Once you figure that out, select a DAC optimized to work with your streamer.  Understand the difference between asynchronous and synchronous DACs and why those differences are important in terms of synergy between your streamer and DAC so that you avoid paying for features on your DAC, for example, an expensive proprietary clock, that you may not even use because clocking maybe controlled by the streamer.  

 I'm only suggesting that you take some time learn about what you have and how to move forward such that you maximize your system's performance and not waste money.

Purchase components that will grow with your future purchases. I bought my Martin-Logan CLS Is speakers over 35 years ago and they are still world class today in terms of what they do well (midrange that's hard to beat at any price point).  Buy once, cry once.

I read through this thread pretty quickly and might have missed it--but I didn't seen one mention of Roon. And that's the part of this equation that I can't wrap my mind around. Does everyone here stream via individual providers' apps (ie, Qobuz or Tidal), or do they use Roon?

Another issue that vexes me is cut-by-cut or album-by-album listening (the de facto standard on Qobuz, for example) vs a "curated" stream of music a la the disk jockey days. I want Qobuz catalogue put together for me in endless streams of topic-relevant selections (ie, Baroque vs Bach vs Romantic vs Impressionist vs choral--just for classical, though there are other categories for other music).

Still no streamer, though I have excellent NOS/R2R DACs and DDCs here. 

Welcome to streaming, you now have subscription access to a library full of everything, in their best original versions, and Spotify and Tidal also win the contest by creating custom playlists based on your favourites.  Long story short, all default streaming players suck as players, compared to what standalone players can do, but fear not, because the best file player is Audirvana, and they have come to the player rescue by supporting Tidal streaming, and therefore letting streaming get close to standalone playback quality, using them.

Also, I hope you're using the mac versions of everything, Windows will make all your sound be constricted to coming from a Windows keyboard, though you could still think it's good inside of that,, but a Mac won't sound wrong.  Linux isn't wrong either, but even Mac users don't think Linux gets any software support.  Audirvana has a Linux version that sounds good, but it's buggy, and has to be controlled by a phone's tiny remote control screen, instead of a big monitor.

Oh, and for what it's worth, a power cable upgrade on my pc gave me deeper, wider ranged, and bolder original versions of both audio and video out of it.  All cabling matters.

Digital output by a PC sucks, compared to the dedicated and simple audio gear.  Your next gear could be a DDC, (Digital-Digital-Converter), placed in front of your DAC.  That will rebuild your non-audiophile digital output as a hi-fi device with a better clock, to send to your DAC, and make it sing at it's best original signal reception.  After you love your DAC, upgrade it's cheap and noisy PC reading with a DDC.  A DDC is the audio experts giving you a device that beats the digital output you would previously try to get from a sound card.  Just digital output to that, first, it will beat that to your cherished DAC, so hopefully you were already in heaven before getting your DDC, LOL.

Just get everything (requires Audirvana) out of your PC ASAP, Kernel Streaming if you're wasting your time anyways on Windows.  USB handoffs to the audio people, too, that mobo stuff is all junk first.

When I started streaming, I had just the s basic 3-piecer like you have.  After that, I would recommend doing what I did, and upgraded the DAC to one that cost more than I should spend, but fall in love with, to upgrade a system around for some time.  This was all just a short version of years, with names left out to preserve your options.

I read through this thread pretty quickly and might have missed it--but I didn't seen one mention of Roon. And that's the part of this equation that I can't wrap my mind around. Does everyone here stream via individual providers' apps (ie, Qobuz or Tidal), or do they use Roon?
 

@desktopguy I use Roon (lifetime subscription) and HQ Player. As of late, I’ve had to troubleshoot my network and streamer after Roon’s updates which has become a pain. Because of this, I could see my next purchase being a streamer that has both Tidal and Spotify Connect. 

I love Roon; I just wished they focused more on stability than new features that seem trivial to me. 

audioisnobiggie

Welcome to streaming, you now have subscription access to a library full of everything, in their best original versions ...

There's a fair amount of music that isn't available streaming, and what is available on streaming is often the "remastered" version. So you get "hi-res" but it's dynamically compressed, making it neither "best" nor "original."

Don't get me wrong - I think streaming is great. But it's just one option and often not the best.