Hi Will,
Yes, this can be done by the Dual input mixer embedded in the DAP of the SGTL5000.
The Dual Input Mixer can be enabled or configured in a pass-through mode (Main channel is passed through without any mixing). When enabled, the volume of the main and mix channels can be independently controlled before they are mixed together.
Please take a look at page 20 of the SGTL5000 for more details: http://www.nxp.com/assets/documents/data/en/data-sheets/SGTL5000.pdf
Please feel free to contact me again if you have any further question about this feature of the NXP Codec.
Have a great day,
Jose
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