It's as Solandri says.
If the HTS thinks you have a center it sends all the dialogue to the non-existent speaker.
You need to set the receiver for 4.0 operation. That would be for 2 fronts and 2 rears. No subwoofer.
If you value clarity in the dialogue over surround sound effects you could use one of the rear speakers as the center if it's identical to the left and right front speaker. You could still use the one speaker for surround effects.
Usually this is done in the speaker set up menu.
Check the owners manual.
When vocal music is recorded in surround sound, usually the vocals are only recorded onto the center channel. Since you have only 4 speakers, not 5, you have no center speaker, and thus aren't getting the vocals.
It's as Solandri says.
If the HTS thinks you have a center it sends all the dialogue to the non-existent speaker.
You need to set the receiver for 4.0 operation. That would be for 2 fronts and 2 rears. No subwoofer.
If you value clarity in the dialogue over surround sound effects you could use one of the rear speakers as the center if it's identical to the left and right front speaker. You could still use the one speaker for surround effects.
Usually this is done in the speaker set up menu.
Check the owners manual.