That's what I'd want too. It's a real shame Vaistech doesn't make adapters for our LS400s.
The only thing that I have seen that remotely works is an FM transmitter. That is, assuming you don't want to go to the trouble of removing the head unit, which I don't.
Is there another way to add MP3 capability to the stock Nak unit? I have seen the cassette mp3 players as well, and tried one 3 or 4 years ago. It was garbage. Worked less than 1/2 the time.
I'd love to be able to pull a wire or two loose from the dash, and tap in by soldering in an 1/8" stereo input jack, but I think that's beyond me unless someone knows of a tutorial somewhere...