Ran into a limitation with this. While footstep triggering works on 3-d floors just fine, the actual SOUND that's selected is the problem: it will trigger the footstep sound of the REAL sector's floor texture, not the 3-d floor's floor texture.
So if you have a 3-d bridge made out of wood, but the the ground underneath the bridge is made of rock, when you walk on the bridge, the rock footstep will be triggered, not the wood.
I guess it's a
CheckActorFloorTexture limitation.
A workaround to this limitation, if using the above bridge example:
1) Set the real sector's floor texture that's under the bridge to wood
2) Move the real sector's height down by about 1 map pixel
3) Setup another solid 3-d sector in the same sector, this time with a rock texture
The idea here is that, you want CheckActorFloorTexture to check against wood, which is already done on the real sector. However this looks ugly, because you are suddenly seeing a block of wood on the ground. So to get around this, you move the sector down, then mask off the truth with a solid 3-d floor with a rock texture.
Very tedious, but it's the only way.