I just want to let you know before hand that my knowledge is limited in Enneagram as it is just something I have only recently decided to take seriously.
The primary reasons I feel 7w6 over 3w2 for woof is his general behavior:
For instance in music, rather than choosing to be a master of one instrument to indicate prowess, which is what a 3 might do. In his case, he has decided to be a jack of all trades, being proficient in several instruments, but not necessarily mastering them. To me this would indicate 7 behavior of wanting to learn several skill traits and not just be limited with one specifically.
I don't really see him as showing that much 8 behavior so a 6 would make sense as a wing for him, though it may not be that obvious at first glimpse. I think he most likely would be a head type over a heart type IMO. However, 3w2 is something that seems believable, but doesn't strike a chord to me as being his dominant form of behavior, which in that case it is most likely a part of his tri-type.
The main question comes down to is woof a head type or a heart type? I choose head type, but heart type is a distinct possibility. However either way, I'm pretty sure he fits the so/sx type stacking very well.
I used to feel the same way Nico1e, however I've realized that the Enneagram is essential in describing aspects of ourselves that are not adequately illustrated by Socionics. It covers ground on a lot of areas that Socionics fails to deliver despite the overlap and when you include type stackings than it becomes a more than suitable way to complete the puzzle of who and other people are.