So I found this video
a moment ago, a compilation of footage both about and of the Ytse Jam, Dream Theater's first instrumental. There's rehearsal footage and footage from shows spliced together. For the first segment of the song, John Myung is pretty inaudible, but in the second he's pretty audible, even more so when he takes his solo. He shreds it up!
As a bonus, you get a few good looks at Myung's Stingray, the hallmark of his sound pre-Images and Words and pre-sixers. Still can't identify the pickup he added, but you can definitely see it. Looks like a soapbar of some kind. For those who don't know, he ran the bass stereo a la Geddy Lee, Chris Squire, and Billy Sheehan, with the neck pickup going to a clean rig and the bridge to the effected rig.
Pretty cool stuff if you're a Dream Theater fan. At least I thought so.
Hang on a tick...that monster has THREE pickups! Or do my eyes deceive me again?