Depends on what music you play and what sound you're looking for, but I would keep the Emperors and work on getting a great sound out of them unless they're so beat you need to change them.
I would second this.
Here's a quick rundown on the basic remo heads;
Emperor = 2 ply 7 mil film - decent sustain, durable
Vintage emp = 2 ply 7.5 mil - A little less sustain, a little heavier sound
Pinstripe = 2 ply, one 10mil, one 5mil + dampening ring - short sustain, Think about godsmack for sound
Ambassador= 1 ply 10 mil - Long sustain, bright sound
Center dot = 1 ply 10 mil + 5 mil dot - Formally known as Controlled Sound, Same as Ambassador just a little less sustain and added durability
As your using ebony ambassadors for your resonant heads, i'd guess that you want a darker tom sound. If that's true, stick with the emperors and play with the tuning a bit, i dont think you'll be disappointed. But if you are you can go for pinstripes.. Or try your luck with Coated Emperor Xs
That's a hybrid between controlled sound and emperor (the 2 10 mil plies PLUS the 5 mil dot!!) It's mainly used as a hard hitters' Snare batter.. but if you want REALLY heavy tom sounds.. There it is