Have you considered adding a subwoofer or two? I also have the CM4s and lime you I wanted a fuller sound. I added a Sunfire Atmos XT, and then eventually a second identical sub. I bypass the crossover on the subs and run them without a ton of gain, the result is nice tight ample bass. You could get a decent subwoofer with your budget and achieve that full sound.
I like the clarity and stereo imaging I get from the CM4s, they don’t make them with that full front aluminum baffle anymore, and style wise they look very similar to the newer 703 S2 with the grills on.
Anyway, good luck, I’m curious to know how it works out.