I'm curious if any folks have had success with using their headphones in tandem with a subwoofer. You hear a lot about the 6dB effect and how headphones can't really stimulate that low-end rumble sensation, so the obvious solution would seem to be to add a subwoofer. What headphone? What subwoofer? How are you splitting the signal? (digital or analog side) Crossover point and slope? How do you manage levels?