Canuchuck

I have an RM-800 EVO II. I am purchasing a pair of DT 770 PRO Studio Headphones to use for silant practice and am unsure of which ohms to get for best audio results. They are available in 32 / 80 / or 250ohms. The 80 ohm being the truest (flat) the 250 ohm needingthe most power to push. But I am unable to find any info on how powerful the headphone preamp is. Suggestions??