You've fallen for the current marketing scheme that Ambassadors are only good for reso heads. They've actually made great bass drum batter heads since 1957. The only significant thing manufacturers have done that's new is adding that extra ring to the edge to cut down on ring. If you look closely at a PowerStroke 3 - all that head is is an Ambassador with the added edge ring. Take away the edge ring and now you have a louder head because it allows it to be more ringy. Take a ringy bass drum and play it along with guys with amps turned up to 5 and you know what you don't hear? The ring!
You can bring up the durability argument too, but it's false. Ambassadors are tough heads, the slightly thicker Emperor is even tougher. Here's how I look at it, if the drum is a dead thud, and you need more volume, what do you do? You kick it harder, running the risk of breaking the head alot sooner. If the drum is open and naturally loud and un-impeded, you won't have to work that hard to get louder, you can actually use your well-honed bass drum technique and play!
As I said, check out Peter Erskine. Or, for a more recent thing, look up Keith Carlock at the 2005 MD Festival - he was playing a 20" bass drum with regular Ambassadors or Emperors (not sure) and his sound absolutely rocked. It sounded like a bass drum, and not a cardboard box stuffed with a pillow!