I was playing around with my interface box last night and doing some serious listening tests (serious for me anyway). I'm going to have to dig out my sound level meter so I can match listening levels to take a better listen because I couldn't tell the difference between resistor network and no resistor network. A couple of times I even forgot which setup I was listening to and while thinking, "Yea, the dynamics do seem to be a little reduced with the network," then looked down and realized I was listening with just the XLR to banana adapter.
I used my 45 watt per channel 6L6 push-pull tube amplifier and the 12.4 decibels of attenuation (R2=6ohms, R3=2ohms) moved my maximum listening volume from 9 o'clock to 11:30 which is about where I wanted it. I never had a noise floor hiss issue with this amp so no difference there. If you're running a 100+ watt per channel amp you may want to go with R2 of 7 ohms and R3 of 1 for 18.3 dB of attenuation. After a couple of hours of listening the R2 6ohm 5watt resistors were not even warm to the touch, but that is with a pretty low wattage amp.