Ok, I'll give Asio4all a try if all else fails. To be honest, I don't really know how these could help, since the Traktor comes with a high-quality external sound card built-in, and that is the one that gets used when playing. So I don't really understand how the drivers of the internal sound card come into play, but if they refer to them in their own troubleshooting guide that must be for a reason.

The problem is I cannot make changes and then simply play something and listen if the problem is still there. Sometimes the problem only occurs once for a few seconds hours into my set. So this is going to take some time to completely troubleshoot.
To be honest, I have good hopes things will be solved already with the changes I've made so far, because before that LatencyMon immediately turned red and gave an alarm messages the moment I started running it. With the changes I've made so far, I can play for about 15 minutes before a warning is shown. Warnings also don't automatically mean hearable glitches, only that you're in the danger zone. But even then, in 95% of the cases there was nothing wrong to hear at that time. So maybe, just maybe, the problem is already fixed. Only by doing a looooong set, I'll be able tell for sure.

I'd still like to get that Speedstep issue fixed though.