No it cannot accept HiRes.
I had the AA DAC1-mk3 and the Weiss DAC2, I have not heard the Bryston or BelCanto dacs. I used a Legato usb to spdif convertor between my MacBook and the AA DAC1 mk3. In my opinion you need to cleanup the signal before it hits the AA Dac1 mk3, the Legato works great for me. I felt the AA was more musical then the DAC2, I felt they had the same resolution, but the AA had a larger soundstage and was warmer - which is to my liking.
I currently have an Audio Research DAC8 at home and a Legato/Havana in an office system - I regret selling the AA DAC1 - mk3, I would be using it in the office system. I really liked the AA Dac1-MK3 but for some reason I thought I needed HiRes capability - I don't !