standalone chips?

There are...
For basic decoding you will need a Crystal S/PDIF receiver chip to convert the S/PDIF into the various data streams (clock left/right etc)... then maybe an external oversampler(although they are inbuilt to the dacs these days...mostly)...then into the 24bit 96khz dacs...then into low pass filter to analog eary pleasure..


but for 5.1 decoding.. Still need the receiver and also you will need a DSP such as the Analog Devices Sharc Melody...which has the power to decode all the channels and oversample and feed to dacs (from a 1 - 5Mbit/sec S/PDIF data stream)....

but you have to have a licence with Dolby Laboratories to do so ,and for Analog Devices to release the source code for the DSP's to you

It would be interesting to know how much a licence would cost... a licence from Philips/sony to make your own CD player used to cost $20.000