TSM2 works again in v13s.
Anzovin never published any commentary on how it does what it does. An industrious person might examine it closely and ascertain that, but I suspect David's info will point you to a similar outcome.
But "auto-balance", don't bother recreating that. It's really just averaging the hip position between the feet, which is almost never the right place for a good pose. Do not use auto balance. A good animator knows how to create balanced poses, a bad animator can't be helped by auto-balance.