What happens when a 6th level Brawler has Improved Two-Weapon Fighting and Flurry. Does the Brawler now have the ability to make a second off-hand attack as part of the Flurry?
Does the Brawler have to use a second limb?
When concerning Unarmed Strikes, the Brawler version of Flurry only offers two things: The ability to use one limb, and the TWF tree of feats. (Full Strength on off-hand attacks is also granted under Brawler's Unarmed Strike).
The extra attack comes from the free feat. To exclude the use of the Improved Two-Weapon Fighting feat would be the same as excluding any "exterior" feat, such as weapon focus or power attack, from the attack, would it not?
If you already have improved 2WF at lv6 then you get nothing at lv8.
If you have improved 2WF at lv6, it works the same as if you had waited till lv8 to get it in class.