I wouldn't do it. You're more than likely going to ruin your amp.

If the speakers are different impedences it would be like using two different sized tires on your car, a taller one on the left and a shorter one on the right. It'll work for a little while but eventually something will break due to excess stress.

Even if they are the same impedance it doesn't mean that they're the same. Their paramaters may be completely different. The exact same way that two rims may be the exact same size but will more than likely have different weights and offsets.

I hope you know a little about cars lol. If you do, then you know exatcly why I wouldn't do it.