Oh contraire, I have EP350 and it has both high and low level inputs.
He's saying high level in and out, not just in. I'm also assuming an actual cross-over, and not just a low-pass filter. That way the sub can control what signal gets passed on to the speakers, rather than the full frequency range.
A speaker cabinet, and driver does constitute a band-pass filter anyway. It's more a matter of getting a smooth match between the two (the electrical filter in the sub, and the physical filter in the speaker).
