It our be great to understand how all of that works. I hope someone responds. 

The low 30 ohm impedance output of the Benchmark as source, into the high 100K ohm load of your amps easily meets the general rule that load impedance be at least 10X source impedance, or more. We are only looking for voltage signal transfer, not power transfer (current), so a high load impedance to source impedance ratio is desirable.

The Benchmark has output to 1.77 volts, so your amp sensitivity of 1.24 V is also no problem. They should be able to reach full power output.