I'm in the same exact boat as you - I have both the Node 2i and the SU-9. There's a lot that I was able to glean/adapt from that post about the X16 as it applies to the SU-9. Essentially, (I believe) we are getting a max of 24/96 sent to the SU-9 via coax, but oddly only if we disable the MQA output of the Node. When I've put my Node into MQA External DAC mode, I never get more than 48k on the SU-9. Disable it, and boom suddenly I'm getting 96 on MQA material (The SU-9 displays Hi Res and 96k). My hunch - we are getting BETTER than "regular" 16/48-44.1 audio, but perhaps not the absolute best possible? To my ears, Tidal MQA source material with this DAC and streamer sounds wonderful and noticeably better than regular "HiFi" Tidal, but of course that's entirely subjective. I personally have a very low FOMO level about this setup.
For the folks who want to use Tidal and want the full MQA experience - I think the best thing to do is wait a month or two. The Tidal Connect feature keeps getting more robust, but it's not quite there yet. The only thing I can't do is send my Tidal session from my Android phone to my laptop, or vice versa. Maybe this is different on Mac/iOS? The upshot is this - once Tidal Connect can work reliably between my phone and my computer, I'd definitely consider getting a small fanless mini PC and using that as my streamer. Those things cost ~$150 depending on options, and once I have it setup with Tidal, I can connect it to my SU-9 via USB, toss it in my cabinet with all my other gear, and control it remotely. Since the SU-9 accepts Tidal MQA over USB (and so few streamers have USB out) that seems to me to be the best possible option, if you truly want more than what you can already get out of the Node 2i/SU-9 currently. I personally would not spend big $$$ to get a DAC that might give you a higher sample rate on MQA, mostly because I think there will be much cheaper routes to accomplish this in the future, with the DAC I already have.