Hi, Geoff,
This topic has been addressed several times previously. Please see these threads:
http://e2e.ti.com/support/data_converters/audio_converters/f/64/t/202197.aspx
http://e2e.ti.com/support/data_converters/audio_converters/f/64/p/573/2164.aspx#2164
http://e2e.ti.com/support/data_converters/audio_converters/f/64/t/2469.aspx
http://e2e.ti.com/support/data_converters/audio_converters/f/64/p/122792/437988.aspx#437988
So, as you can see, TI does not have a good solution for this in a simple stand-alone IC.
I was hoping that someone in the community would chime in and point you in the direction of an IC that does what you want. I have seen many customers in China using ICs to do essentially exactly what you want, but I don't know the manufacturer or part number of that chip.
-d2