Just found this PDF on the DM70s, the specs are limited (i.e. no impedance curve) but it does state that the nominal impedance is 8ohms. Given that the SA-8800 is comfortable at 4ohms it should be fine driving them.
DM70 PDF
...and some specifications for the SA-8800:
Power: 2 x 80 W into 8 Ohms
Freq res: 10 Hz-20 kHz
THD: 0.005%
Inputs: Phono 1, Phono 2, Tuner, AUX, Tape 1 Rec/Play, Tape 2 Rec/Play, Pre/Power: Pre OUT / Power Amp
Controls: Loudness, Filter: Subsonic/High, Phones, Cartridge Load, Tape Monitor, Tape Duplicate, Interference Filter
Dimensions: 420x380x150mm
Weight: 16kg
Miscellaneous: 4 x AC Outlets, AC: 110/120/220/240V, 50/60Hz