Larry,

Obviously you must be... In your 50's, Have Used Headphones at High Levels for Extended Periods, or Have a Tin Ear! ;-)

I always thought it was easy to hear the difference between the same song on FM, and on a CD.

Here's an article I found after doing a Google search, it's talking about how Stereo AM is achieved, but in doing so discusses the Audio Spectrum of FM as well.

[Link: geocities.com]

Note that below 50Hz the Audio Spectrum rolls off at roughly 50 dB in one decade! Note that nearly the same thing happens above 15KHz. This effect is present because without it, one station would interfere with the other if they are spaced apart the minimum allowed amount. (This happens very often, the channel spacings are fully allocated by the FCC.) So, you're not going to find an FCC approved modulator that will give 20Hz-20KHz audio frequency range using FM or AM modulation.

This can be done, just not legally in the AM/FM radio bands.

I think the best bet for audiophile quality transmission is to transmit the signal digitally, and amplify at the Sub. I've not seen a solution meant for this. Has anyone else seen such a device?