The 9NTs are considered 8 Ohm speakers, but they drop to under 4 Ohms at low frequencies. I was hoping that the higher current output of the 7100 would help.

Here are the ratings for the 3801 for comparison.

Rated power:
105W into 8 Ohms 20Hz - 20kHz 0.05% THD
140W into 6 Ohms 1kHz 0.7% THD
Dynamic power:
140Wx2 into 8 Ohms
210Wx2 into 4 Ohms
240Wx2 into 2 Ohms

If I remember correctly, the 3801 actually outputs something like 45W per channel if all 7 channels are used.