I don't know this amp, but I do have 704's. The answer to your question will depend in part how big your room is, how loud you play your system, and what kind of music you listen to (for example, do you listen to music with a lot of heavy bass).
My 704's are powered by a 200 wpc amp that has a wattage indicator lights. The speakers are in a 14 x 21 room that's acoustically lively. When I played organ music or classical orchestra/chorus pieces VERY loudly, the lights would show a maximum of maybe 75-100 wpc momentarily
. Now that I have a sub in this system (with crossover set at 50 Hz), none of the wattage indicators ever go on because the sub is doing the heavy lifting. So I'm not certain if 70 wpc is going to be enough because there are too many unknowns. Or if someone had one of those nice impedance/phase angle graphs for the 704's (like the ones in Stereophile), you'd have a much more definite answer.
AT&T U-Verse Northeast Ohio
Denon x4000, Carver m1.0t, Samsung LED TV, B&W 704 mains, two M&K subwoofers, Oppo 103, Roku 2, etc.
Headphone system: Sennheiser HD600, AKG K702, Hifiman HE-400i, Marantz HD-DAC1 (also used for music playback in the main system, Marantz CD5004, Denon DVD-3910