using two outputs from a dac?

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. 

Thanks, all. My DAC doesn't have a volume control but I can certainly turn off my preamp or switch the input on it.

Thanks again!

I had a Tisbury passive preamp (= RCA switch) for that purpose. Typically you don't listen to speakers and headphones at the same time so an A/B switch will work fine without worrying about impedances.