tweaking book (koma-script) class?

I'm trying to create a new class, based on the book (koma-script) 
class so I can make a few small changes.  But I haven't figured out 
what I need to put in my new .layout file to have it be recognized. 
I've got the following line now,

#  \DeclareLaTeXClass[book (koma-script)]{poh}

but after I reconfigure lyx my poh layout shows up as "Unavailable: poh".

I've looked through the latex and lyx file structure, but I can't 
find where the book (koma-script) class is defined, so I can't figure 
out how to refer to it.

Any hints would be greatly appreciated.

TIA,

Kevin Horton