A preamp can both boost the volume and/or color and/or EQ the sound. One of the intereesting things about the F-2B is that the flat setting is 2-10-2 - in other words, you can boost the bass and treble, while the mids mostly get cut. Even setting it flat, with the volume set at a reasonable level, it will probably affect the sound - in a good way!
RE: blowing up speakers/amp, between the volumes on your Series I and on the F-2B, I don't think you would have any problems - just don't crank them all at once!
I love my F-2B - use it in the studio as well. If you do any recording then that makes it even more desirable, IMO. I usually go bass-->F-2B-->direct box, with great results (IMHO again). Of course, if you are going to use it live, you will need to rack mount it, and plug it in somewhere.
(Sorry to go on and on about the F-2B, but it is one of my favorite ever pieces of gear - I actually own two! One on the west coast and one on the east coast for when I go back there)