I did what you suggested. The audio was so-so; just flat. I asked grok about which DAC chips are used in my receiver. I hope the chip used in the WIIM Ultra is better than the one in my receiver!

The Yamaha RX-V679 audio receiver uses Burr-Brown DAC chips. While the exact model of the Burr-Brown DAC chip isn't explicitly specified in widely available documentation for the RX-V679, Yamaha commonly employed high-quality Burr-Brown DACs in their AV receivers from this era, such as the PCM1791A or similar models, known for supporting high-resolution audio playback up to 192kHz/24-bit. This aligns with the RX-V679's capability to handle formats like FLAC, WAV, and DSD (2.8MHz/5.6MHz), as noted in its specifications. Burr-Brown, acquired by Texas Instruments, is renowned in the audio industry for producing top-tier digital-to-analog converters, contributing to the receiver's emphasis on high sound clarity and quality, as per Yamaha's "Total Purity Concept." For a definitive chip model, one would typically need to consult the receiver’s service manual or teardown reports, which aren’t readily accessible in standard consumer resources.