Thanks for all the great responses! The woofers do appear to be the originals and appear to be in good shape (the suspension is very tight - hence I guess the low amounts of bass by design). It's not just the low bass I'm concerned with, but the overall woofer output. The horns are very much an in-your-face sound while the woofer output (all of it) sounds like it's two rooms away.
My friend took the speakers back, but I'll suggest resealing the cabinets. There have also been a few recommendations to recap the crossovers. Do they have a profound impact on bass output or is their failure primarily evident in the highs and mids? I've tried them hooked up along with my sub, but my sub is a big bruiser and is primarily good at adding the lowest octave even when I set the crossover quite high. The Heresys seem to want something to bolster the whole woofer range in order to keep up with the horns. In terms of placement, I've tried the speakers on the floor, but they were 12-18 inches away from the wall. I'll try pushing them back up against the wall and nearer to the corners.