If it ain't broke....then why fix it? What speakers are you driving? 400 watts might be overkill for most typical 6" woofer type domestic speakers. Unless you are driving big pro type woofers (large 4" voice coils) much of that "extra" amplifier power may simply be turned into more heat and thermal compression or just may not be needed.
...just a thought. $7000 new is a lot of doe to replace your exiting and working CA-300 even if it is old.
...just a thought. $7000 new is a lot of doe to replace your exiting and working CA-300 even if it is old.