Thanks Gary! I've done some experimenting and, to answer my own question, have come up with a solution that is fairly simple:
The "tracks" that make up a user song are divided into two parts: A and B. A is called the "System Track" and B is the 16 user tracks. You are correct that these are all midi channels and do not have the capability of recording an analog signal plugged into the instrument or mic inputs. BUT, once you have all the A and B channels you want recorded in "song sequencer" mode, you can then re-record them as an "audio file." This uses the "Audio Record" button, rather than the "Record" button. At this time the previously recorded midi tracks can be played and accompanied by ONE external analog input! I stress ONE because I don't believe that, for example, a bass guitar part AND an electric guitar part can both be recorded this way (unless there are two of you and you do them simultaneously!) . It's a one shot deal. SO...when I need more than one analog input I am going to use my stand alone 8 track digital recorder to lay down all those instruments / vocals into one signal, then input from that device into the single analog input on the keyboard. Of course syncing these signals together is the trick, but with a few trials on when to push the buttons they mesh together well.
On another related "note" : During my song sequencing, I was wanting to use the accompaniment (one key "chords" that have piano and strings combined) and those only work in A mode - "System Track". I haven't used any of the rhythym accompaniments yet, but I'm sure those will also only be available in A mode.
This way I have all the parts I want recorded into the keyboard so I don't have to mess with a computer (I don't have a laptop). There is a little noise associated with the analog signal, but what's new about that!? lol.