OP
Nice Subs, however:
Your Subs Manual does NOT specificity mention line in/filter remove low bass/line out without low bass to the preamp or integrated amp. AMP to speakers AFTER sub
They may have it, implied, but I am not sure.
"Control Settings for Stereo Receiver or Pre-Amplifier Most Stereo Receivers and Pre-Amplifiers do not have bass management. Instead you will use the Left and Right full-range outputs and make adjustments through the DSP amplifier on the subwoofer. Be sure to connect both Left and Right outputs to the Left and Right inputs on the subwoofer. Set the Low Pass Filter to “On” and adjust the Crossover Frequency and Slope to achieve a smooth blend and transition with the main speakers. Once blended, adjust the Subwoofer volume to match the volume level of your main speakers"
...................................................
To speakers after sub gives the speakers a break, but does NOT give the amp, a break, thus the amp is always trying to produce low bass which gets filtered by sub to speakers.
This does not help a low powered amp do a better job (i.e. only powering upper bass/mids/highs with slightly inefficient speakers.