Your whole concept is mismatched, hmm I would have expected better, matching loudspeakers placed at the same height, its not too difficult to do, matching LCR!
The tone, when you listen to pink noise from LCR, what happens is that it changes tone slightly. To EQ correctly takes days and a golden ear. If you where to placed LCR outputs into an audio mixer lines 1 2 and 3 and just use s single output to one loudspeaker and balance the level of the three channels with an SPL db metre. What you’d hear is an indistinguishable sound with the automatic pink noise cycling the fronts or LCR and surrounds.
If you don’t believe try it, it takes skill to get it done right!
My JBL Control 5 LCR each have there own amplifier for LF and HF which is controlled via a (loudspeaker management system) with there own EQ and it sounds better than most, now then.