hi,i own a kenwood ka4520 amp.it was bought new and still serves me for many hours of continious play[many times overnight]very loud.lately i think that it sounds a little empty in very high levels so i am thinking of changing the aged caps with new ones.i wouldlike your help here,what caps to change and wich ones could be upgrated.i would also want to know if i can make the amp a bit more powerfull,perhaps changing output transistors ,but without sacrificeing sound quality.thanks in advance