Very interesting question. The Gallos are known for their good bass response IIRC and a well respected loudspeaker. I don’t think the NAD will take you where you want to go and would be a side step. Class A/B amps are really the kings of good bass control and slam so I would think about a good 200 plus WPC A/B amp. The big power supplies and large capacitors tell you they are designed to store and release power. Also keep you DAC separate, digital designs are still improving so there is no need to tie the two components together. I would just change out your amp and give that a try first. Optimize then think about adding a sub later on.
P.S. Are you using the SA bass amp?
P.S. Are you using the SA bass amp?