"Stacks" specifically refers to the stacks of speakers used as the main PA. There are two stacks, each about 20 feet high, on either side of the stage. If you're too close to the stage, all the sound is going to be over your head. If you're in the spot in the front of the balcony, the sound is hitting you directly.
I went stealth at Webster because even though the band is taper friendly (they are on archive.org), the venue is often difficult with tapers.
In terms of the balcony, there are seated risers near the back, but you would be in front of those. If you were on the same location on the floor, you'd have the bar at your back. That might be ok (I taped Flaming Lips from that spot), but you'll deal with a ton of nonsense on the floor--people yapping, moving around, and generally acting like asses. There's a 30 second cell phone conversation on my Lips recording from that spot!
Good luck!
Thank you guys for the new tips!
danlynch: what exactly are stacks? When you were at Webster Hall did you have to go stealth? For clarification on the location you mentioned, it's on the balcony level, centered and behind the soundboard booth? I remember there being a small platform where people used it as seating a little behind the soundboard booth. Any idea how the sound would be if I were in the same location but on the ground floor rather than on the balcony?