amplifier output balance

In my home theater, the L+R speakers are Acoustic Research (Teledyne) AR9 driven by an Adcom GFA-585 amplifier while the C speaker effectively is the top section of an AR9 driven by the bridged channel of an Adcom GFA-2535 crossed over at 200Hz. Audyssey XT32 on my Denon AVR-X4000 balances...