Here's a
video of one. Can't see much except that he's using a canister filter. In the comments he says there's a hole for a power filter.
Also found this info in a review.
It has four holes in the top for a heater, filter, and two small holes that I have used for my airlines. The min opening at the top large enough to get all of your decor in. The filter opening is large enough for an Emperor 400 filter.
Found a pic in the reviews
here. Scroll down a bit and click 'next page'. It's in the 7th review. Looks like a hole for a heater and a wide slot for a HOB. He's got two HOB's in that one slot.
HTH