The wood of the cups in the above picture is walnut, also have 2 rosewood and 2 mahogany. I had one cocobolo but sold it as a SennGrado build which my friend really loves.
When doing the sorbothane mod make sure you cut them in to quarters after you glue it on, seems that it works better at vibration reduction that way. As for cutting venting holes it depends on which driver you have, some have venting from the factory so any additional usually does not work out too well, the most I've ever done is 3 holes, more and the bass gets boomy to me.
@dbaker1981
, looks like the start of a nice setup, this is what I was listening to earlier this evening when a few friends were over drinking some wine: