Digital inputs to zone 2 out

Hi, apologies if this question has been asked before. I have an Onkyo HT-RC360 receiver and an external amp (carver a500x) that I'd like to use to drive my main speakers. Ideally, I would simply connect the zone 2/preamp out from the Onkyo to the carver to drive the speakers.

My problem is that the Onkyo only outputs analog sources to zone 2; is there any way to get around this restriction?

For example, would there be a big loss in quality if I connect the headphone out of the Onkyo to the power amp? Or the headphone out of the onkyo back into an unused input of the onkyo (say tape-in) and then the zone 2 to the power amp?

Thanks!