The impedance of the speakers is different, therefore load is different. Replace center JC-1 with one of the others and run your system. If the new center amp runs hot, then it is the speaker load making the difference. If it is not hot like the original center amp, then you would investigate the difference between the amps.
Parasound JC-1 variations
I installed the 3rd JC-1 yesterday. It drives the center channel, and the sound of the 8 Ω KEF R600C now matches that of the 4 Ω 107/2s quite well. But this JC-1 seems different form the pair I’m using to drive the 107/2s. In high bias mode it runs hot to the touch, whereas the LR pair are just warm to the touch. If I set the bias of the new JC-1 to low, it is also just warm to the touch. Reviews and a couple of posts at AVS have noted that the amps run hot, but I thought the 107/2s might be an especially easy load coupled with the moderate levels of music I prefer may have accounted for the mild warmth. Now I wonder if the pair of amps I bought to drive the 107/2s may be running in low bias mode even though the switch is set to high bias. But those amps sound great driving the 107/2s. Would I notice any difference in sound between high and low bias at moderate levels?
Also, the blue light of the new amp is much brighter than that of the other two amps and is bright whether powered up or not — red lights of all the amps follow the same pattern of being bright when on and going to dim when off.
Also, the blue light of the new amp is much brighter than that of the other two amps and is bright whether powered up or not — red lights of all the amps follow the same pattern of being bright when on and going to dim when off.