The battery capacity does not affect how much current is sent to the emitter. So having 1400 mAh batteries in parallel doesn't mean the P7 will see 2800 mA of current.
I suggest you do more research. Start with Stephan's thread in the 'Homemade / Modified' forum on his P7 Mag build.
Like Drewfus says - you seem to be getting confused, mainly between mA & mAh.
If you have an emitter drawing 2800mA of current that is powered by AAs in parallel then 2 x 1400mAh cells will have 2800mAh which means that they can supply 2800mA for 1 hour. If you use 2 x 2000mAh Eneloops then they could also supply 2800mA, but for almost 1 & 1/2 hours. For whatever you are trying to do the Eneloops would be better!
Also:
1 x 1400mAh cell can supply 2800mA - but it would be drained flat in 1/2 hour. 4 x 1400mAh in series can supply 2800mA at 4.8V for 1/2 hour.
If you read up on this and understand what I am saying and why then you will have a much better idea of what you are doing and how to do it.