I just bought a pair of Westone UM2 IEMs (Sweetwater has them on sale while they last for $179). As I have never used IEMS before, other than my audition I just had , I have two questions: 1. Which is better at giving you a good seal on stage - the foam or the rubber tips? 2. How sturdy are the cords - in other words, should I buy an extra to have if these are likely to break? Thanks.