This is the most straightforward solution. You can purchase an RCA to SPDIF converter online or at most electronics stores. Simply connect the red and white RCA cables from your TV to the converter, and then connect the SPDIF output from the converter to your surround sound system.
Option 2: Use an HDMI audio extractor
If your TV has an HDMI output, you can use an HDMI audio extractor to separate the audio signal from the video signal. This will allow you to connect the RCA cables from the extractor to your surround sound system.
Option 3: Use a digital-to-analog converter (DAC)
If you have a high-quality DAC, you can use it to convert the digital audio signal from your TV to an analog signal that your surround sound system can accept. Simply connect the SPDIF output from your TV to the DAC, and then connect the RCA outputs from the DAC to your surround sound system.
Option 4: Use a 3.5mm to RCA cable
If your TV has a 3.5mm audio output, you can use a 3.5mm to RCA cable to connect it to your surround sound system. Simply plug the 3.5mm end of the cable into the audio output on your TV, and then connect the red and white RCA plugs on the other end of the cable to the corresponding inputs on your surround sound system.