The 600 ohm Beyers are really designed to be used with desktop headphone amplifiers which can output at least 3 Vrms or more.
I would go with an amp which can output 8 Vrms to avoid any clipping when listening to music recorded with 16 dB of headroom.
8 Vrms should reproduce peaks has high as 116 dB SPL, assuming Beyer's sensitivity numbers are accurate! i.e. 96 dB = 1 mW