the PREs on the US428 are not really built for super strong input.
The manual states over and over again that this product is not a true mixer so when you put a condenser MIC on the PREs of this machine, you don't get the same effect that you would get if you plugged into say a MACKIE 1202. So if your not geting the level you want in the program that you are using with the US428... you might want to purchase a small Mic Preamp like a TUBEmp to boost your signal...