Getting a shell on serial

I'm trying to use grml as the base for a hardware validation USB key on a machine which
has no video at all, and is accessible through a serial console.

After yanking the boot.msg splash screen and adding console=ttyS0,11500n8 to the append
line, things are promising (moreso than knoppix which had serial support as a module :( )

The issue that I'm having is that even if I use the 'serial' cheatcode (in addition to
having added the console bit to the append line), I'm not getting a shell on the serial 
console.  I get as far as:

   [ ok ]hing for device(s) labeled with GRMLCFG.
  *   Floppy device detected. Trying to access floppy disk. (Disable this via boot option: noautoconfig)
   [ ok ]devices with label GRMLCFG found.
   [ ok ]hed execution of main grml startup.

(minicom messes up the pretty formatting)

And then nothing.  This is the point at which I would normally be getting a prompt and be
on my merry way.

What's the trick to getting it going?

(If I boot the same USB key on my desktop, using the same cheatcode and append line, I
  get no boot progress to screen [all going to imaginary serial], just the grml.org logo
  in the upper left, and then suddenly the normal shell)

Any help would be greatly appreciated.