You are correct, the LiPO PCB Lite is only an audible or visual alarm to a indicate that a single cell has dropped below 3.0V steady state, meaning that it is effectively dead.
IF you want your AEG to stop firing, the other board I make will be of interest to you.
You have to have a MOSFET Trigger for the PCB V3.X to control the firing of the AEG. I am assuming that you do not have a computerized MOSFET Trigger like an SW-COMPUTER (and that you do have a MOSFET Trigger), therefore you would need the "Trigger Mod" which would let the PCB V3.X directly control whether or not the AEG fires. If you pull the trigger and the PCB V3.X sees that a cell has dropped blow 3.0V steady state, it won't let your AEG fire, thus stopping the battery from further discharging.
Here is a link to that PCB (as with Trichrome's post, if the mods deem this is advertising by posting a link of where to get this product, please by all means remove it): http://projectwolfdragon.com/Products/PCB_V3.X.htm
TONS more information on that board and the Trigger Mod are on that page, just look through the manual and you will see wiring diagrams as well as logic diagrams.
It does cost a bit more, but the control and isolation circuits are the driver for the price.
I do not frequent these boards very often, if you have questions I can be found at the airsoftmechanics forums or just send me an email (you can find that address on my site).