Ah, by the way, I'm agree to type Frank Zappa, Iggy Popp and Eminem as ISTPs. Eminem is also a 6w5. David bowie is more likely an F.
*OMG, I've just wrote that and I've felt a compulsive need to play guitar, shit!
Really? Zappa I'm not as surprised about, but Van Halen seems really xSTP
One of the extremes to look at that helps between ISFP and ISTP is objectivity vs. subjectivity. ISTPs think much more objectively. They tend to orient towards accuracy above all else.
I used to take lessons from Chris Broderick from Megadeth who's an ISTP. I used to get creative with my interpretations of counterpoint harmony for example, and he would criticize me for not doing it the right way. He also put a lot of stock in learning to read music and learning proper theory in general. Very much by-the-book and very much about accuracy.
Van Halen had a reputation as a student for his 'creative interpretations' of the pieces he was learning. To him, he was playing what sounded right and as he famously said, 'if it sounds good, it is good'.
The two approaches come down to either doing things 'the right way', which is objectively accurate, vs. doing things the way they 'feel' or 'sound' right subjectively to oneself.