How do these measurements relate to the front USB input or using the streamer services like Tidal through ethernet connected internet? I don't know if it's different (should be it seems) than the tested inputs HDMI, Toslink, analog. Thanks
Keep in mind that AVRs (and related integrated 2 channel amp such as Yamaha's A-S801) can have two separate DACs for different inputs. As far as I know, for HDMI inputs, the main and better DACs such as the AK4458 and ES9006 are used.
If you use the front USB input, Ethernet (network streaming), or even optical and coax, then all bets are off and the signal may be routed through the lower grade DACs such as the PCM5100 or the slightly better PCM5101 in the integrated amp such as the Yamaha A-S801. For Z2/Z3, chance is good that the lesser DAC would be used, such as the case for D&M, Onkyo and Yamaha's.
In some cases, such as Yamaha's, even for the main zone, they would use two different ones, the better DAC for the main 7 channels and a slightly lower grade one for the remaining channels. For example: the flag ship RX-A3080 has the Sabre ES9026 Pro for the main 7 channels, and the ES9007S (same as the 9006) for the remaining channels, and then mostly the PCM5101 for the Z2/3. 3 different DACs!! It's all about cost, I assume..