The DAC operates at 8fs, thus the first image is centered around 352.8kHz. With 16-bit resolution, the image should be filtered approximately 96db. Taking the effects of the sample and hold into account, reproducing a transfer function with the shape of a sinc, the first 40dB of attenuation is reached at the edge of the band at 332.8kHz. (sinc(pi*f/fc)) Thus an extra 60dB of attenuation is needed to reject the image. This circuit filters 60dB at fc and combines the differential output to a single output. The output is muted using a relay.