Just do this. Level match the underseat gain to equal the spl from your center @ driver's ear height. That should then be preset for the r4's. report back.
I think the center is strong vs the oem because of the sensitivity difference. I think a matched frontstage will be golden.
FS:Sub Amp - works w/ Technic harness! MRD-M300 - cheap
DON'T BUY FROM RAF555!!!! Promised fix! - strung me along til Paypal dispute period expired!