I must admit, some of the drum/source sounds i have used in the past can be made to sound realy good even when they sound shit to start of with. I know what you mean about what you put in is what comes out but I also think sometimes low quality stuff can work well with small amounts on certain sounds. I think the main problem I have is processing/e.qing the life out of my tracks. The sounds I sometimes put in can also cause me problems. Like having a hard kick n bass thats sucking away all the power from the mix. I like what you can do with F.x esp pitching and lowpassing sounds. Sometimes its worth boucing some of the main percusion and pitching them around and having them layered up somewhere in the back with reverb/delay. It helps fill out the bandwidth of the mix. Oh, and try gates on kick drums too!! :) :) :)