How are most audiophiles going from streamers to DACS

Optical should be the best in theory, but it's probably the worst because there isn't a good interface available, as far as I know everything in audio is toshlink.

Optical for a CD transport, coax for anything else. 

Agree with reclocking.  The transmitter and receiver are your limitation, therefore avoid bandwidth limited optical and go USB, possibly coax. Coax is TEM00 and USB is twisted pair, at least it better be.  But this is digital so the cable bandwidth is not that critical as analog, and if you mismatch cable impedance, which is never perfect, your error correction from cable reflections, unless your connection is under 6", should give you 100% of your signal. I get no errors in my hi res system. 

  avoid bandwidth limited optical and go USB

I've tested all of them and have gravitated to I2S

what part of "his streamer only has coax and optical outputs" are  you all having trouble with?

I started with the Node2i, connected via both Coax and Toslink to both a  Sony AVR and then a Marantz unit that were "supposed" to support Hi Res.  Both companies tech support knowledge about HiRes and connectivity was pathetic.  I ended up with a NAD t758 v3i - with a
BluOS module (with WiFi dongle/Bluetooth dongle) installed.  The dongle connects to the module on the NAD via USB.  Runs all Hi-Res streaming services including Tidal's MQA (let's not debate that here, it's more hype than actual performance worthy) via the BluOs android app.  I also stream digital files from my PC - those files were my library of SACD's and DVD-A's that were converted to FLAC files.  Easy breezy.  Speakers are all Klipsch including a pair of Atmos.