In this case, I recommend reconnecting this same amp to the towers and connecting your multimeter across the speaker terminals (positive to positive, negative to negative). Be sure to switch your multimeter to the DC setting. Take a few different measurements.
DC at very low volume
DC at medium volume
DC at loud volume
Just in case there is a significant DC offset, do this quickly. A DC offset will not take out a woofer immediately, it does take some time for the voice coil to heat up.
Post your measurements and then we can take the next step.
another option if you like, is to send the amplifier to me and I can test this for you with proper equipment (oscilloscope + power resistor bank for a static load). However, you would be responsible for all shipping costs which could be quite expensive these days. I have done this in the past for other customers and I don't mind it at all. I miss working on amplifiers.