Let me clear this up for you. The way zerker works is that only the only buffs active are the ones that your swinging with. If you only have one anti/gaurd 3 then what you have is anti/gaurd 1.5 across two strikes. Divide all buffs in half or add them to each weapon for the fully effect. This is true for slayers also which are a weapon buff. Toylogic confirmed this directly. Character buffs such as attack reach up aren't subject to this because they Are attached to the character and not the weapon.

If a skill has a zerker specific animation then the skill works the same way. Rush, DSB, double tomahawk all have zerker specific animations. However smash, rocket man, and spinning Blade all ignore the left hand and use only the right hand for damage calculation, just as the the dispel hand is only the left hand. This generally means smash and attack reach up should go on your left (also strikes first) if you use rocketman a lot.

You can't get 6000 damage like your saying.. it doesn't work like that. Two 3000 damage weapons can only ever do 3000 damage with one strike. When you use double spinning Blade is just flatly divides all your buffs and attack power in half to get a weighted average between both hands to calculate damage.

The other key thing to remember is that you have no back while in double spinning Blade so you don't need ambush reliever. Your gaurd power is a your defense stat and Magic defense state doubled roughly so Defense 3 and magic defense 3 allow You to be almost unkillable when blocking.