The simplest way would be to go from the headphone output from the TV into a splitter, then running one side of the splitter to amplified speakers and the other to the sub. Once you balanced the speaker and sub volumes, the TV volume would be your control for sound level.
If you go from optical, you must have a DAC to convert the signal to analog for the sub. I suppose there may be a pro monitor that has optical input and a sub output.
Will the volume control of the TV will effect the optical out. I don't think so, but don't know. If not, you may not be able to control level or mute sound without going to the speaker's volume control. Hopefully someone can address whether or not the optical output is controlled by the TV volume level.
Part of the issue is getting a setup where the volume will apply equally to the sub and the speakers. That is why the headphone output with a splitter may be your best solution.
Another approach is to get something like the OrbAudio Booster amp. I suspect you are looking for more capable hardware, but this 25RMS WPC stereo amp has optical input and a subwoofer output and adds a remote control.
Edit:
The Emotiva PT-100 may be your best option for an inexpensive, but capable pre-amp. It will do the conversions you want and provide a remote without a ton of "features" that you likely don't care about. At this point, it technically is a pre, but it is more DAC than pre to my mind.
https://emotiva.com/products/pres-and-pros/pt-100