Mark, don't worry about it. Although THX and others have found that 80Hz is about the best compromise, being high enough to relieve the speakers and amps of a significant part of the lowest bass load but not so high as to make the sub easily localizable, 90Hz is very little different. Don't even think of passing up the benefits of an HT receiver's bass management and instead forcing the speakers and amps to carry the full bass load(and trying to adjust the typically inaccurate internal crossover on the sub).
