Oh the slippery slope You have a pretty nice setup to be sure. I'm in a similar situation, and my last step is deciding on a streamer.
I have a Tube pre amp and a Tube amp from the mid nineties. Question was, how the heck can I stream hi rez music's to it. The simple and easy way was getting a Audioengine BI high quality Bluetooth music receiver for casual listening. I connected it to my pre amp via RCA and I can send any music from my phone to the B1 like Tital, Amazon HD, Spotify and YouTube etc. For more serious listening and out do the DAC in my Oppo BD 105 (which I use alot) and take my sound quality up a notch, I bought the Exogal Comet plus Dac and that has balanced outs and I run those into my pre amp ( ARC LS15) and it sounds very good indeed! The Audioengine BI also has toslink out, so I could run a toslink cable from the B1 to my Comet DAC for even better sound quality. For streaming I'm strongly leaning towards the Innous Zen Mini as it also will rip CDs and I like that option, as I have some rare CD's The Innous also has a high quality internal DAC, so maybe no need for an external DAC in your case.
As you've already figured out, there are so many options, and very good recommendations. The difficult part, what will work best for you and your system. Happy hunting!