My friend has an Orange Crush Pro 120 solid state amp. It's specs state that it can run 8ohm minimum and it has two output jacks on the back in parallel. He has a matching Orange 16ohm 2x12 cabinet that is presumably 2 8ohm speakers in series. He had two extra 12" 16ohm Celestian speakers that I wired in series in a new cabinet. This gives an equivalent resistance of ~11ohm which is safe per the amps specs. however, is there any issue with the fact that the two cabs are not equal impedance? I know the 32ohm cab will not be as loud but anything to be worried about beyond that?
It's fine. Play it.
as long as the 16 ohm cab can handle atleast 2/3rd of the output power (although the amp won't be reaching its full 120W anyway, more like 90W or there about) its all right to run those in parallel.
cheers