hmm... so the +6/+1 type bonus attacks are only for the primary hand, yes?
In that case, with TWF and ITWF, the Primary hand would get 2 attacks (2 from BAB ), and the Offhand would get 2 attacks (1 from TWF and 1 from ITWF) ?
If you wield a second weapon in your off hand, you can get one extra attack per round with that weapon. When fighting in this way you suffer a -6 penalty with your regular attack or attacks with your primary hand and a -10 penalty to the attack with your off hand.
Your penalties on attack rolls for fighting with two weapons are reduced. The penalty for your primary hand lessens by 2 and the one for your off hand lessens by 6.
So Primary hand and Offhand would both be at -4, assuming both weapons were NOT light....
Improved Two-Weapon Fighting [General]
In addition to the standard single extra attack you get with an off-hand weapon, you get a second attack with it, albeit at a -5 penalty
-5 from the highest attack bonus available, in this case the +6 ? Or from the current Offhand attack?
So, assuming I can count... At a +6/+1 BAB, 2 weapons, TWF and ITWF...
1) Primary at +2 (+6 and then -4 from TWF)
2) Primary at -3 (+1 and then -4 from TWF)
3) Offhand at +2 (+6 and then -4 from TWF)
4) Offhand at -3 (+2 as normal, but -5 from the ITWF)
That look right? Attack #4 looks weird...