i'm going to make some assumptions here... that there is nothing wrong with the incoming fios signal, that the tv reception is clear, that there's nothing wrong with the hardware whether it be the tv or supplied equipment from verizon and what you want is just to be able to hear the audio more clearly.
if this is the case, get an a/v receiver and a pair of decent speakers (or use the audio equipment you may already have,) connect the audio-out from the verizon stb (or dvr) to one of the receiver's audio inputs. ideally, use a digital connection, either a digital coax or digital optical cable or depending the receiver's features you can use an hdmi cable from the stb/dvr to the reciever, then, another hdmi cable from the hdmi-out of the receiver to the TV to carry the picture. (again i make an assumption you're using a hdtv and not an old standard crt.)
i like the optical cable for the audio. if you go with the hdmi cabling route be sure to consider the receiver's cababilities. the hdmi-out on the unit should support at least 1080i (or 1080p) and ought to have audio return support through hdmi.
you can go for an home theater setup with center and rear speakers along with the mains, and add a subwoofer for good measure to hear and feel the sound effects.
use some older audio equipment that's lying around and just hook that up with two speakers using the left/right (red & white) audio output of the stb/dvr.
you can even just get better speakers for the tv. something like a soundbar unit. (you'd still hook it up to the stb/dvr, digitally of course.)
whichever route you take, the idea is to bypass the TV's speakers with something that will give you much louder and clearer audio.