I can hear a little livelier sound at 0dB than -20dB but -10dB is much worse and my 0.5m cable has total of only 6pF/ft x 1.5ft=9pF.
Are you using the calibrated output - bypassing the DAC1 volume control?
What you report strongly suggests that the device (power amp or preamp) that you are connecting the XLR outputs of the DAC1 to - this device has a rather low input impedance (much less than 20K). I'd check this angle out - many power amps have simple input attenuators (rather than variable gain) which may lower the power amp input impedance (depending on the power amp volume/trim settings and the design).
Also if you are using adaptors to take XLR from the DAC1 to RCA then be aware that pin 3 must be left to float or yo'll get distortion.