Even disregarding the subtleties (of which there are many), these two
factors alone make HD AM dramatically superior to analog AM stereo.

If IBOC were running pure compressed digital audio, that would be
true!! However, IBOC on AM is only 36 kbps, and only maintains
accurate frequency response up to _5 kHz_ -- all audio above that
point is "spectrally replicated", i.e. "faked" based on harmonics of
lower frequencies. To my ears, it sounds like the treble has been run
through a cheese grater!

Analog AM may have a more limited high frequency response, but at
least it is ACCURATE treble response -- not screechy, gritty, heavily
artifacted treble that is about as pleasing to the ears as fingernails
scratching on a chalkboard.

A new comparison between analog AM Stereo and digital IBOC/"HD Radio"
AM can be found on this site:

http://www.geocities.com/kevtronics

Download the audio samples of both, and compare!

p.s. One thing I can say, however, is that your Optimod 9100-B2 is the
best-sounding analog AM audio processor that has ever been built --
and, of course, it really shines with AM Stereo. Stations which just
want to be LOUD use the 9200... but stations which want to be both
loud AND good-sounding almost universally use the 9100.