Both the E Series E100 and E50 are rated at 17 watts per channel, this is the same whether you have 1 pair or 2 pairs (wired in parallel) of loudspeakers attached having an impedance of 8 ohms.  A 6 ohm nominal impedance loudspeaker pair can be used and would also achieve an output of 17 watts per channel.  In all instances the the distortion would be @ < 1%.