blanka, I think you answered your own question. I was getting sound to work at first using another method too. In fact, I have used four or five different methods to get usb sound working in some capacity, but it wasn’t until I reversed my other attempts and followed the instructions in the link to create /etc/modprobe.d/alsa-base.conf that the delay went away.
Right now, however, I have the broadcom audio enabled again going to the built-in 3.5mm jack and my USB dongle is unplugged. I discovered that the NORMALIZE audio setting in advancemame was the cause of crackling. Once I turned off normalization in the GUI, and permanently with this line in advmame.rc: “sound_normalize no” the crackling stops. I am testing whether or not I even need USB audio.
Anyway, try the technique outlined in the link above and see if that works better.