hi i have a marantz sr53oo reciever which is 90 watts per channel [ 6.1 ] and it says on the back speaker impandance for 6 - 16 ohms speakers but i have

psb stratus bronze [ 4 ohms ]
psb c5i [ 4 ohms ]
yhamaha souronds [ 8 ohms ]
koss center suround [ 6 ohms ]

so my question is am i damaging any part of my system by mixing the impendance of the speakers and the reciever or did i buy the rong recevier for my bronzes or can i fix the problem by buying a sepret 4 ohm amp


matt

thanks in advance