I don't doubt jishaq's 200Hz crossover - there were some really unwise bass management choices made for multichannel analog outputs on both Pioneer and Panasonic players. (Panasonic liked 120Hz at one time, and may still favor that.) Your Pioneer may not have the same crossover point. With the 990, though, you likely have the speakers all set to "large" - which should bypass any such crossovers inside the player, allowing the Model 990 to get the bass management right.

Which makes me wonder... If the 48av's bass management is defeatable, it wouldn't be an issue for users pairing it with the Model 990. If the bass management is part of the analog circuit, though, there's nothing to be done except shrug and question the sanity of whoever at Pioneer signed off on that particular design decision.