DAC Connections to streamer?

It could very well depend upon the digital input circuits of the DAC.  The best have a USB input that is self powered (not using the 5V from the cable) and have two femto clocks for the families of 44.1K and 48K digital sreams.  Such a circuit should favor a USB input.

That being said, some devices, like the Oppo I use for audio/video, don't have USB outs so spdif or optical is used.  Much to my surprise, I found that an inexpensive Cable Matters Toslink Cable (a Duster recommendation) from Amazon outperformed an expensive all silver spdif cable.  You never know!

Have a chord tt2 dac and only has optical, usb and bnc. Strange no coax.

BNC is coax with a different connector (75 ohm). Chord has been using them for quite some time, as do other manufacturers.

Coaxial bandwidth so much better vs optical.

Optical can easily handle 24/192 with the right implementation and parts (i.e., Chord) and a proper glass cable. Which sounds better? Well, that’s quite subjective and depends on your taste/preferences and, of course, the implementation.

BTW, I use a Sonore microRendu which is USB-out only. Fabulous sound quality and it’s their least expensive in the line.

The new Sonore microRendu 1.5. Is due out in oct for $399. Ie Ethernet in and usb out.

Not sure how it allows connection between bluesound and a chord tt2 dac.  

You can't connect the two. The microRendu would replace the Node 2i as your streamer. While I realize you currently own the Node 2i you asked about streamers which use USB-out and is the reason I mentioned it. You don't exactly seem pleased with your streamer at this point and if your displeasure continues you can always sell the Node 2i and purchase a different streamer with USB-out, like the microRendu. If the new microRendu is better (or equal) to their discontinued model it's a great price.