hi, is there any effect on my system with different impedance in my speakers?

i have a current setup of:
onkyo tx sr 501
left & right speakers monitor audio, 6 ohms
center definitive tech c2, 8 ohms
surround - def tech pro monitor 100, 8 ohms
sub -def tech pro sub 100
dvd player pioneer dv 533k

pls help?