is the audio low, making it hard to hear?
is the audio muffled, making it hard to hear?
if the audio is low, i would suggest a compressor.
if the audio is muffled, a stereo widener can sometimes help.
if neither one of those help, you need audiophile speakers.
can you plug in the audio into a computer, then output the audio into the television?
thats how you use a compressor and/or stereo widener IF the soundcard has such a feature.
sometimes televisions have a 'virtual surround' setting.
try turning that on to see if the vocals get any better.
maybe you dont need to upgrade the speakers .. maybe the speakers you already have need a little bit of help.
you may find yourself buying upgraded speakers, but the vocals are distorted at the source.
could be the actor/actress
could be the microphone
could be the analog to digital convertor used when recording the audio
maybe the software used to manipulate the audio before it is considered 'final'
did you connect the new soundbar to the television or to a cable/satellite box?
maybe it's the televisions soundcard causing the problem..