how do I access the SPDIF signal from my phone my galaxy s has the option to have 5.1 surround enabled. what plug on my phone produces the digital audio signal to carry the 5.1 surround?
is this option only available through bluetooth or can it be used through the headphone port or USB port?
The Samsing Galaxy S series has a virtual surround, not a true surround. Therefore there is no way to get multichannel audio out of the device, only analog stereo.

Source: Phandroid, Unleashthephones, Intomobile