The optical cable is the problem.
Optical is a pure, unmodulated, digital connection. It is just a data stream, there is no "power" behind it in terms of amplification, and it is audio only, without any type of control signals. That is why there is no response to the tv remote from the soundbar. It is simply not possible with that arrangement.
The ONLY way a tv can affect the volume of an attached soundbar is:
1) If both tv and soundbar are HDMI ARC and HDMI CEC capable
2) The hdmi arc connection is used from the tv to the soundbar
Your soundbar is a very basic model and is not capable of using hdmi connections. To do so, you'd have to return/exchange it for a new/better soundbar. I can recommend some options, if you'd like.
Otherwise, your options are to attempt to program the cable remote to operate the soundbar directly (unlikely to work)
OR to purchase a more robust, true universal remote to control all of your devices, such as a logitech harmony (click here for example) that will work for all of your devices. It is programmed through an easy to use software program on your computer, which downloads the most up to date remote and device codes from the internet, so it is virtually guaranteed to work with all equipment. It will also give you easy to use macro functionality, so you can press a single button to watch a movie for example, and it will turn on the dvd player, tv, and surround system, tune to the correct inputs on the tv, and start the movie playing, etc. Because of the online database with specific codes for each model, this type of remote has much greater functionality than the basic universal remotes (including the one that came with your system.)
Best regards, ***** ***** for the news,