Elevated sub - yes or no?
 

Recently moved to a new house and, due to space and layout constraints, I currently have one of my subs sitting on my entertainment center. I have to say it sounds pretty decent -- no rattles, even when it's really thumping.

I thought I'd read that having one sub out of place with the other can help smooth out peaks / nulls. Think I'm getting any benefit with the subs in this layout?

Since every room is different, you can't really know how it will improve or diminish the sound unless it sounds or measures badly with respect to other placements. If it sound good, I would just keep it. Have you measured it?

I haven't measured it. Since I don't have too many options in the room I'm not going to bother trying different locations and measuring the results. I was just curious to hear feedback on having one sub positioned higher than the other...

Nice headphones! I have the ATH AD700 myself and it's been a great, I especially love the weightless feel.

Elevating the second subwoofer should be fine, you will get a slightly different frequency response depending on the height of the elevated subwoofer. What is the height of the elevated subwoofer?
Also, what is the distance from ports in the back to the wall with the elevated subwoofer?

The AD700s are incredibly comfortable! I do wish they had a fuller bottom end though -- I end up turning the bass tone control up a few dB when I listen to them...

The right sub is sitting an entertainment center that is 24" high, so the center of the driver is probably at 32" or so. I'm toying with the idea of putting the subs on either side of the fireplace, with the speakers just outboard of the subs and the entertainment center along the right-hand wall (assuming my speaker cables are long enough!).

I believe that your current subwoofer location is fine, the height you mentioned shouldn't cause any cancellation problems. Like ShadyJ mentioned, unless you measured or can hear any dips in your frequency response I think the elevated VTF-3 Mk4 should be fine where it is.