1) there's nothing to "get." Listen to the Yellow Shark to see how Zappa's path, as a non-academic modern composer, was almost the ONLY path with which to avoid the kind of studied modern-ness that has so severely harmed Amercan music (and which I hear in David Baker's work, to cite one old academic; also which I hear creeping into a fair amount of good non-academic musicians' work like that of Rosenwinkle and some others) -
2) in person the band was a fantastic amalgam of chaos and control - a perfect Zappa creation. Hard to replicate on recordings (best concert: 6/14/68, McMillan Hall, Columbia U).
3) repeating number one - Zappa's music has an edge and life that separates it from the "serious" world. And much as he complained, it owed a lot to the vernacular, rock and roll world for this,
4) Buy the Mystery Disc. A Perfect intro to FZ
5) as as a guitarist, I think FZ was over-rated; listen closely and you'll hear that he's a pattern player, like a lot of guitarists
6) to me (and I know this is a minority opinion here) Beefheart is a big nothing, a one-trick pony who made his point and than made it over and over again. Still, he gave up some good ideas. Just did not turn them into silk.