Brian Davies made a comment that I thought was telling. He said that given two systems with the same driver, whatever EQ is provided to make the amplitude response equal will make the transient response equal too. So it's probably not an apples and apples thing - If a system is optimized so transient response is improved, it pays for it with less extension. If bass extension is made deeper, whether by acoustic device or electrical EQ, then the transient response will suffer by the same amount.

Wayne