That is a huge space for those speakers, and the impression of diminished bass is relative to prior powerful amps, perhaps making more bass out of those pairs of 6.5", but with more distortion than you are/were aware of.
I would want larger woofers, (I have and would want 15" in that space). I always like mid and tweet horns, then, how much power to drive them? And, you say solid state, but I would want tubes, made affordable and more practical by efficient horn speakers.
My 14 x 24 room, I use 45 wpc tubes, that never seems 'not enough', but I don't listen to cannons and crashing highs anymore.
Definitely consider more power than generally needed to have reserves for instantaneous demands.