I agree with the C1 + sub route, or one like it. My C4's are in a 16' wide x 40' long x 9' high room (big volume) and they sound very good except I would give them a "pretty" good down low. The bass response is uneven from 30-60 Hz (big dip) that seems to plague a lot of rooms. Two subs can help you tune this better by moving the subs around independant from the mains, which are placed to image the best (not to improve the bass!). And, most subs can be tuned by EQ. I'm looking at subs for my C4's for this reason!
As for volume, most speakers in modern hi-fi (no tone controls at all!) sound best when they exceed the fleetcher munstrum (spelling?) pressure level in the bass. This is the point where your ear becomes linear across the typical sound spectrum humans hear. The C4 seems to become "flat" in the bass around 80-85 dB to my ear. So I agree, that this speaker needs to voice some. But, if a speaker sound good low, it's probably too much bass turned up. Your ear loses a lot of sensitivity to bass at low volumes, so to sound good quiet, it's really not "flat"in the bass, and remains so as you turn them up. Such as it is without any variable SPL control anywhere.
Get what sounds best where you listen the most. I listen at 80-85 dB average SPL most all the time.
As for volume, most speakers in modern hi-fi (no tone controls at all!) sound best when they exceed the fleetcher munstrum (spelling?) pressure level in the bass. This is the point where your ear becomes linear across the typical sound spectrum humans hear. The C4 seems to become "flat" in the bass around 80-85 dB to my ear. So I agree, that this speaker needs to voice some. But, if a speaker sound good low, it's probably too much bass turned up. Your ear loses a lot of sensitivity to bass at low volumes, so to sound good quiet, it's really not "flat"in the bass, and remains so as you turn them up. Such as it is without any variable SPL control anywhere.
Get what sounds best where you listen the most. I listen at 80-85 dB average SPL most all the time.