Hi 2x6spds,
I presume the sub out on the Antique Sound Labs is not already low-pass filtered. If it is, set the Velodyne crossover at its highest frequency, then follow these instructions.
Begin by setting the crossover at 80 Hz, and then experiment by raising or lowering the setting while you listen for a seamless transition from the M3's to your subwoofer. You want to avoid a hole-in-the-bass between 150 Hz and the useful low-frequency limit of the Velodyne.
A test CD with spot frequencies is especially useful for these tests; if you combine it with the Radio Shack Sound Level meter, you can usually achieve a smooth transition.
Regards,
