This link should help you.........Download the handy LED Calculator.
Click here 
From 6 x AA (7.2v) you could run 2 LuxIII's in series (Assuming 2 Lux's each with a Vf of K - 3.6v ea)
If running LuxIII's in parallel - you have to worry about using up the excess voltage from the cells by inclusion of resistors....What a waste of energy!
Best thing to do is run pairs of series connected LuxIII's in parallel. (2 Lux's in series gets the voltage just about spot on - so you dont need to worry about the resistors)
How many parallel sets you can run depends on how much current you want to run and how much current your AA's can supply at a given loaded voltage.
The more sets you run the more voltage sag - the less Lux drive level.
Cell quality is the biggie here. Other factors such as switch resistance and differing Lux Vf's will all have an influence too.
The same story goes for 5 AA cells - but to get a useful drive current you would need to be using lux's with a Vf of 'H'.....Due to the lower voltage.
Do try the LED calculator link....Its very good.
After all that......Best advice.....Use drivers to regulate the current.
Tim.
