Logic has three types of channel strips/tracks. You need to be recording MIDI (and more importantly) playing back on a software instrument track with a software instrument instantiated in the input slot in order to hear any MIDI audio.
Thank you, Doug. You solved the mystery. Also, thanks to all the other users who took the trouble to read my tale of woe, and offer help.
For the sake of anyone else who's stumped by this, here's the relevant paragraph on page 67 of my
Getting Started With Logic user's guide:
"Audio Instrument
This Audio Object supports the use of software-based instrument plug-ins. These plug-ins include those that are built into Logic, plus third-party Audio Unit instruments. Although the Audio Instrument Object looks similar to Logic's other Audio Objects, it supports MIDI note input, which the others do not. This enables appropriate plug-ins to be played via MIDI, just like an external MIDI synthesizer, sampler or module. The corresponding Audio Instrument tracks in the Arrange window allow you to record and play back MIDI Regions."
No mention of this 3rd type of track is made in chapter 2:
Getting to Know Logic's Arrange Window. Audio and MIDI tracks and regions are described there as if they are completely separate modes with no overlap... no possibility of playing MIDI on an audio track. Because I am upgrading from a much older version of Logic (Logic audio 3.5), I had no clue about Audio Instruments and Audio Instrument tracks, so I was skimming over everything that had to do with audio tracks and their channel strips, in my search for a solution. It didn't occur to me that audio inserts might include software instruments, playable via MIDI. In Logic 3.5, inserts were all audio effects, of one kind or another.
My setup worked out-of-the-box with Garage Band, but that didn't shed any light on my problem because in Garage Band the New Project and New Track wizards always provide the right type of track for MIDI, automatically loaded with one instrument or another. In Logic 7.2, MIDI tracks load by default with piano, guitar, strings, etc., but "audio instrument" tracks are left undefined. So, when I moved my MIDI recording onto one of these tracks, there was still no sound.
Anyway, despite the long learning curve, I am very happy to be up and running with Logic again. I couldn't afford a Mac when Emagic stopped supporting PC's, and I've been stuck for years with a Windows editor that can't even "select all following," which, for me, is essential for any serious work with a matrix or score editor.
Maybe I'll even go back and do some more work on my music for the
Song of Songs, although my style and interests have changed a lot since then.
But, right at the moment, I'm just jazzed to be playing with all these cool new sounds!
So, thanks again!