Many TVs these days have eliminated true line level audio outputs, and have only digital optical S/PDIF and analog headphone outputs, like your Vizio TV. (They are assuming that most users will use the digital audio output into an AV receiver.)
Because the headphone output is amplified somewhat (as oposed to line level audio outputs), you may find that you need to limit the volume control on the TV so as not to overdrive the external amplified speakers. Hopefully you can find a level match between the TV's headphone output and the speaker's volume control and still have full volume control range with the TV's remote.
Both Audioengine speakers are very nice, but keep in mind that the bass output difference between the A2 and A5 are not subtle due to the A2's 2.75" woofers versus the A5's 5" woofers and corresponding cabinet size (the tweeters are essentially the same).
Steve