I have my sound bar Samsung hooked to my TV fine with sound. My Android box is hooked up to my TV via HDMI but the sound bar doesn't have another slot for anything else. I have a spot for AUX IN on the bar and the box has SPDIF and AV.
You should not need any additional connections.
Sound from the android box goes to the TV via HDMI and from the TV to the soundbar with the connection you already have. Check the audio setting in the android box if you don't get audio from the soundbar.
Worse case you can use the audio part of the AV output into the aux input on the soundbar.