The key component of the synth solo in the Cars "Let's Go" is the filter envelope changing for each note, with the envelope being reset for each note. This doesn't need a hex layer - it's a solo synth. It absolutely DOES need the filter envelope to be triggered on each note event, and the envelope needs to be programmed to give the right resonance and change through each note. I found a couple other sites with the same question - one of them goes into quite a bit of detail about needing oscilator sync capability and how to set the sync. http://forums.musicplayer.com/ubbthreads.php/topics/2132225/synth_sound_for_the_Cars_quot_ This article claims it was a preset from the Prophet 5, 'Sync II' patch. Which again points to oscillator sync - which is not going to be in chapter 1 of a synth programming tutorial. Here's Jordan Rudess demoing and describing oscillator sync on the Moog Sub Phatty:
Note that this is topic 8 of Rudess' explanations. Note what he says (It's one of the most advanced functions.....) at about 1:50 - 2:15 or so he says this. I can't determine if the XW-P1 had oscillator sync or not at present, but it's pretty fundamental to the sound of that lead.