I have this cab too. I've always thought Eminence Deltas would be an almost direct replacement, but I'm no expert. I've heard good things about Delta Neo 10s too, could shave a bit of weight off. You should make sure they'll work well with the Ampeg before spending any money though. edit: meant the Eminence Deltalite 2510, not Neo.
I'm not sure if Eminence Delta is the proper replacement, 210HE is 250W cab and Delta speakers are 200 or 300W each... maybe it wouldn't be a problem, I don't know.... I found Deltalite speakers in pricelists only as 8ohm version, which is then impossible to combine two of them and get 8ohm... any other suggestion ? thanks