I will give this a shot (this is stretching my battery knowledge and I'll be pleased to hear the real answer when the experts chime in)

I was not aware that there was a micro pack with 2000, but can we use a pack of 6xAA's with a capacity of 2500 mah and compare to a sub C stick pack of 2400.

The sub c is designed for a higher dischare rate (possibly 50 amps) the AA is designed more for capacity and may sustain a discharge rate of 10 amps. If you have a application that uses the battery very slowly, then sure you can use the smaller cells, but on a regular power model that runs 10-15 minutes will pull the voltage down very low on the AA's and ruin them soon.

If you were interested in why this happens I think it may have to do with the cells diameter where a larger diameter cell gives a higher discharge rate and a longer cell gives more capacity. That's about the extent of my knowledge of cell design