Some models of Skybox receivers have a digital output. You'll have to check the back of the box to see.
A 2-channel digital audio signal, or a encoded DTS or Dolby Digital surround sound audio stream.
A coaxial digital output (usually an RCA jack) can connect to a digital optical input using a coaxial to optical digital converter. This is a small box that goes in between the two products.
Digital audio stream
There is a combined headphone and optical digital audio output (minijack) socket. On the current iMacs it is the first socket on the back.
Sony/Philips Digital Interface. Provides digital output and the best signal quality. Connects to an external home theater audio system.
Yes, you can use a digital cable to connect the audio output of the TV to the receiver. This will allow you to amplify the sound from the TV's tuner.
To generate audio signals from digital signals received from Headphone's output voiceport on computer.
Digital audio recording is taking a sound and turning it into a string of numbers then rebuilding the vibration from those same numbers. The numbers are generated by direct measurement of the audio signal. Digital synthesis is where numbers are constructed or generated by multiple calculation that are based on the user input. the numbers are treated like a graph of sorts of the output waveform. The output signal is generated from this graph.
Bluetooth is a digital communication interface. It tends to be used for audio signals more than other applications so it is often perceived as carrying analog audio. Despite the appearance, it is definitely digital and not analog.
Speakers are analog devices. There is no cable and connector that will connect a digital audio jack to a speaker without a digital to analog conversion and an amplifier. If the audio output is digital, you will need a compatible amplifier that has the same digital input. Then you will need to link the amplifier to the speaker with exterior grade cable.
The LG LHB335 only has an optical digital inputs. If your cable box has an optical digital output, connect it to the Digital in #1 (TV) with an optical cable. If your cable box only has a coaxial (RCA) digital output and you want to use the digital audio connection, you will need to purchase a coaxial to optical digital converter. The Monoprice 2947 is less than $20.00.
It's not as simple as making a cable that fits. Digital audio cables and digital signals, both coaxial and optical, require a digital input. You need to convert the digital signal to analog to work with older receivers. These are available (Google Digital to Analog Converter or DA Converter). Just about every device that has a digital output will also have an analog stereo output, which will work with your old gear.