So today, I had my dash apart for an update of the cubby illumination, and I came up with an aux-in solution:
I'll keep the cassette adapter, primarily because the sound is adequate, and I'm not skilled to solder wires to the circuit board (as in the article linked above). The wire from the adapter to the jack remains hidden behind the radio and comes out inside the cubby. Nothing new so far.
The annoying part of this solution was the whirring sound from the cassette deck, especially when only navigation or speech is played (rather than music). So I thought it might work without that noise if I simply cut the wire to the motor. That was a fail; the motor is needed to push that electromagnetic whatchamacallit into the cassette. However, once that's done, the input works without the motor!
In other words, for the cassette adapter to function, the motor needs about a second worth of power; then it's no longer needed.
Those familiar with my mods know that I have an unused momentary button in my center console (which used to be an O/D off button). I wired that button to the motor of the cassette deck. Now, when I begin using the cassette adapter, all I have to do is push the button for a second for the deck to engage; then...no more whirring sound.
Hey, I realize this may come across like a hack job. But it functions, and I can maintain the stock radio look.

