using two outputs from a dac?

Thank you both so much. @erik_squires--that's reassuring, at least in the sense that I'm not going to fry (or blow up!) anything. @mksun, very bright and pretty cool to have such a bespoke cable. If this setup becomes permanent, I'll consider one for myself.

Usually all output are live unless your piece of equipment has output selector switch. 

It’s best to contact Bryson for their recommendation. It all depends on the output stage design. Some manufacture design separate output circuitry for single end and balanced output. Henceforth both can be used simultaneously. Other simply tap the positive leg on the balance output and therefore doesn’t recommend using both together.

just my 2 cents.

Provided that you don't have a turntable, if your DAC has an analogue volume control, as does Audio Analogue's DAC, you don't need a preamp. 

I stream from my Aurender A30 to both my Luxman preamp and my Pass Labs headphone amp with no issues.  I do have whichever system I am not using switched to a different input. I can’t notice any degradation in performance. Aurender did confirm this setup was acceptable.