Quite honestly a subwoofer is the wrong direction if you want more bass definition. You need to increase the power at nominally 100Hz +/- 20 Hz for bass impact and definition. A subwoofer is poor at reproducing those frequencies.
If your speakers have bi-wire terminals and your woofer to tweeter crossover is low enough (e.g. 2Khz max.) you might consider adding another amp- e.g. parasound a23, and connect the Cronus sub outputs to the inputs and connect that amp to the woofer terminals.
The CM has relatively low gain so you would need to adjust the gain on the bass amplifier by ear or measurements in order to match the tweeter level.
Ideally you do this in a three-way system where the tube / low power amp drives the midrange and tweeter. However there is no reason it couldn't work in your situation.
The tube amp will not even break a sweat while the solid state amp should deliver all the bass and drive you need.
I have done this successfully and am considering doing the same thing with my CMII.
If your speakers have bi-wire terminals and your woofer to tweeter crossover is low enough (e.g. 2Khz max.) you might consider adding another amp- e.g. parasound a23, and connect the Cronus sub outputs to the inputs and connect that amp to the woofer terminals.
The CM has relatively low gain so you would need to adjust the gain on the bass amplifier by ear or measurements in order to match the tweeter level.
Ideally you do this in a three-way system where the tube / low power amp drives the midrange and tweeter. However there is no reason it couldn't work in your situation.
The tube amp will not even break a sweat while the solid state amp should deliver all the bass and drive you need.
I have done this successfully and am considering doing the same thing with my CMII.