On my Mackie Forum, there is a fellow Cubase user running a Mackie1640 firewire mixer. He is also using a LIne6 USB device. Apparently both are connected and he can quickly switch to either device - but I am not exactly clear on the entire path. He made a youtube video here: http://www.youtube.com/watch?v=EqEOFuaHlkE&feature=youtu.be
Would you mind taking a look at it and telling me what you think is going on with his recording process? His thinking is that the Mackie has a problem with latency as you change the sample rate of the driver that Cubase cannot correct. Its weird to watch because I have a Mackie 1640i mixer and I do not have this problem.
I have suggested that he unplug the Line6 device such that Cubase cannot find the Line6 driver and try the test again. I also suggested he tick the metronome track he has pre recorded into musical mode in case he has something odd going on with his project and the time signature. Any ideas would be helpful, he says his English is not that good.