Doing the crossfeed button only set the RCA output level to 3v which is higher than the usual cd player output level which is around 2v. If the input sensitivity of the integrated amplifier is not great, it would result in clipping.
I find there are 2 methods two connect hugo to integrated amplifier:
1. connecting hugo to line level input of the int. amplifier but reduce the volume of hugo so it will output at a level which more less match the line level input sensitivity of your int. amp. In this case, you are not using hugo preamp, and you can use the volume control of your int. amplifier. This is similar to connecting a CD player to Int. Amp. But reduce the volume of Hugo to avoid clipping.
2. connecting hugo to line level input of the int. amp., but set that input as home theather bypass (if your int. amp has this function). this will result in bypassing the preamp function of the int. amp. and using the hugo as dac and preamp. volume control of the int. amp. will be disabled hence you need to adjust volume on the hugo for listening.
My int. amp has the home theatre bypass function and i can compare the sound quality using each of the above method. In my case and IMO, sound quality is better using Hugo as preamp.