Hi John Deeve, welcome to the forums!
Does the sound card of the laptop must be shut down for the installation or while you are mixing?
I'm not too sure what you mean by this, but the U46 is used while you're during installation and mixing. You can still access your laptop soundcard even with the U46 plugged in.
is there anything that won't work with mixvibes DVS pack 2?
Concerning hardware, nope! Although we are working on getting a couple MIDI things to work more accurately.
How about the reaction time(latency) of the mixvibes on the turntables? Doesn't the program stops sometimes. I have had that with behringer bcd3000 and tarctor 3 LE the program always stopped and blocked.
You can adjust the latency settings to your needs, but if you optimize your laptop (there's a couple threads on how to do that) you should be able to run the 3ms setting no problem, and if that works well you could even use the 1.5ms setting.
Hope this helps!