There is no such thing as a jitter imune dac its complete sales BS, also there are several diffrent kinds of jitter
While I agree that nothing will be completely jitter free, however, in the case of the DAC1, the sales BS is backed up by measurements using audio precision equipment - while not perfect (what is?) the measurements demonstrate what most would call excellent "immunity to jitter".
When comparing good DAC's as you have could it be possible you are hearing small differences between them in the analog output circuitry (op amps) and low pass filter design rather than differences due to jitter?