impedence rise/amplifiers

when playing sine-sweeps (don't ask) I hit a point where the impedence must drop, and the amp switches off because it doesn't like it... it also does it with some songs....

I've had issues with this amp doing it before, only with sealed enclosures... anyway, would it be alright if I temporarily paralleled the 2 channels to combat this?

the amp seems to have alot of protection circuits (considering its over 30years old) so, if it doesn't like it, I'm sure it will tell me...

any thoughts?