There was some occasional occurrence of 'second layer'. Check this thread:
http://www.subsim.com/radioroom/showthread.php?t=131383
Other then that, I'm afraid nothing. But you might still try, DW did surprise me few times. They don't have things they say they have, but sometimes also they have things they don't talk about.
AFAIK latitude has no effect on layer depth, and there is no sound channel. Also depth has no effect (at least on passive sonar). Bottom type does have effect, but very straightforward, it simply scales everything down as the bottom gets softer.
Edit: my bad, latitude DOES affect layer depth, it is mentioned in that thread.