First, try to optimize the placement of your main speakers and your subs. I like to use the AM Acoustics room mode simulator. Try to keep yourself and all of your speakers out of the lowest room modes.
I am of the school of thought that a higher crossover for subs is best, especially given all the feedback from listeners who started too low. Up to 80 Hz is a good spot. In your case, this will reduce the load on your amps significantly, hopefully making up for the low impedance around 2 Ohms for your mains.
Next, consider sealing your main speakers. This will raise the -3dB point, but also severely reduce distortion and excursion in the lowest octaves. Clean socks work great here.
Lastly, the DSP control over the subs will give you an unprecedented advantage over pure main speakers. Leverage it, but instead of striving for flat, strive for a descending slope from 16 to 80 Hz, about 1.25 to 1.5 dB per octave. Then set levels to taste.