OK, guys, I have been watching this thread, and nobody has yet to hit the nail on the head, so...
As far as I know, there are two A-bomb packs for download here at SOH.
One is from Mark Rude for stock CFS3. For this pack, yes, you need to add effects lines and fxtextues. However, you will have to either make them your self or borrow them from FirePower, as they simply are not included in the pack.
The other A-bomb is a repaint of the FirePower A-bomb, Fat Man, I think. No effects lines or fxtextures come with this one, either.
The only thing you can do, as far as I know, is to go into a FirePower install and make a copy of the effects xml file, open it in Notepad, and find the necessary lines.
The safe bet would be to make a new Notepad document and copy the necessary lines to that, prior to copying them into your CFS3 effects.xml.
Begin the search for those lines by opening up the XDP file of the FirePower A-bomb and look for the effects it calls.
Note: It looks simple in the XDP file, but once you get into the FirePower effects.xml, these things can become a "domino effect", and there very well could be a lot of lines that need to be copied. Once you start, you may have to follow them through the FirePower effects.xml fo get them all.
Once you've done that, you would then have to go into the FirePower effects/fxtextures folder and copy out only those *.dds files that are not in stock CFS3.
You would probaly also have to do the same thing with the sounds.xml file and sounds folder from FirePower to make sure you get it all over to stock CFS3.
Rule #1: Always backup anything and everything you intend to change or replace before you do so. This will save a lot of headaches later on. Good luck.:d