Speaker impedance is nominal, not exact, so either the 2 or 4 ohm tap should work fine. I would try the 2 ohm tap on a couple of speakers first. If the volume is too low, try the 4 ohm tap. A lot depends on the quality of the amp. Some can tolerate low impedance better than others. A 70v system is the right way to approach this. Connecting 34 speakers to a standard amp without some sort of impedance matching will burn it out quickly.I have a Cress 70.7-volt stereo amp and 34 Sony 3-ohm cube speakers. I believe I need to find some step-down transformers but everything is geared for 2-4-8-16 ohm. Any idears?