Looks like the transformer for the R/SR/C is larger than the one for the SR/R in order to keep the VA/ch consistent between channels.

The three channel transformer has three secondary coil windings, while the two channel transformer has two. One coil winding for each subsequent channel. Thus, the bigger transformer.

I hear the right, center and RS louder than I do the other channels.....maybe because they are against the wall. IDK

Have you calibrated the system yet? If not, that would explain why some channels are louder than others. If you have, you may want to re-visit the calibration.