The crossover used when the switch is set to HPF/LPF is at 80Hz. I'd generally recommend making sure that the bass management in the player is disabled, but a CD player shouldn't have that issue. What you may want to do is try some test tones (my Devious Tiny Disc would suffice) to make sure you are providing a signal with content below 80Hz - a lot of music won't dip that low.