Looking for an upgrate from Cronus Magnum

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.  

you guys with experience with the pharaoh- do you think it gives up anything in sound quality to the CM?  
does it have a sound signature?  
what type of speakers pair best with it?  
thanks.  

Hegel integrated power and sweetest.
Best I ever tried from the H80 to H360 all awesome.
Regards 

I am not sure that the problem here falls into tube/ss dilemma, in a strict sense of it. Yes, amp/speaker match etc., of course. Really good tube amp will give you great drive and bass with many speakers. Rogue is an audiophile value company, the expectations should be realistic. At this price level, yeah, I think the OP would prefer hybrid or ss. That's why someone said not to bother with tube rolling. Tube Rogue integrated is not up to the task with these speakers with any tubes. No tubes can compensate for class, class that the Rogue does not have.

I have a Rogue Audio Pharaoh that I have to put up on the site if you are interested. I had the Cronus Magnum and upgraded to the Pharaoh. The first thing I noticed was the increase in the bottom end.