The one suggestion I would make that hasn't already been said is that before replacing anything you try changing the receiver's speaker impedance setting from 8 ohms to 6 ohms, if you already haven't. See page 40 of the manual.
Although the impedance of your speakers is specified as "compatible with 8 ohms," whatever that may mean, it most likely drops down to significantly lower values at some frequencies. Therefore using the receiver's 6 ohm setting might result in an improvement in its distortion characteristics, and therefore perhaps a reduction in perceived brightness.
Regards,
-- Al
Although the impedance of your speakers is specified as "compatible with 8 ohms," whatever that may mean, it most likely drops down to significantly lower values at some frequencies. Therefore using the receiver's 6 ohm setting might result in an improvement in its distortion characteristics, and therefore perhaps a reduction in perceived brightness.
Regards,
-- Al