What happens when I connect 8 ohm speakers and 4 ohm speakers?

I've blown my speakers once already but their fixed, and I am curious about this. I have two 4 ohm speakers (JBL TR225s) and two 8 ohm speakers (JBL 125s). I piggy-back the 8 ohm speakers out of the 4 ohm speakers from one single 3000W amp. Is this safe? Any help would be great thanks.