db,
If you're using the SMS-1 in auto mode, you're only scratching the surface of that unit's potential.
The SMS-1 will output FR <200hz to any video monitor. You could hook that up to get a visual take and see how it correlates with what you're hearing. You'll also see the FR thru the x-over point that you've chosen. If you tweak the parametric DRC settings and slope, phase, etc. (assuming that you haven't already done so) to achieve the flattest FR around that point, you'll hear a really seamless hand-off from the main speakers to the subs.
You should also manually adjust for smooth FR below that point. Unfortunately, Velodyne (IMHO) mangled the auto-correct software and the cumbersome manual set-up is really mandatory for best results.
Marty