Hey, just had to respond. I used to live in a converted Incense factory! It actually wasn't converted too much.. it still had a drop ceiling, cement floors, etc. 3000sq ft. of one giant room.
The place smelled nice though. And with the big huge doors, we could just drive our motorcycles right in the front door and park inside.
But the acoustics were terrible. Drop ceilings + cinderblock walls + cement floors = terrible.
As to your question.. I did a bit of movie watching in the place. I only had a two channel speaker system, but the acoustics really were quite bad, and a bit of a distraction. With headphones, I feel it is important that you have a Dolby Headphone processor.
Basically, it accepts the 5.1 Dolby signal, and then introduces crossfeed, and reverberations to make it sound like you are in a room, listening to 5 speakers and a sub. The effect isn't perfect, of course, but it is FAR superior to simply downmixing to stereo. I'm not sure if there are hardware decoders for Dolby Headphone, but I know that most of the DVD player software for computers supports it (WinDVD, etc.).
If you plan on doing some good headphone movie watching, and bothering people around you isn't a problem, I suggest you check out Dolby Headphone processors (see if your unit has one maybe), then look into getting a nice pair of headphones. The Sennheiser HD600 is one of the phones that they used to do the modeling, so you might do well by getting either the HD580s or HD600s. They are open headphones, so they leak a lot of sound, but in your situation, their openness would mean you could leave the sub on, and wear the headphones instead of the 5 speakers. Then you would still 'feel' the impact of the bass. Sounds like it could be very neat.
Anyway, hope this helps a bit.
Peace,
phidauex