Mcx also optimizes balanced inputs by speeding up non CAST connections to make them sound much faster than non Mcx non cast connections. Don't sweat the tube pre, I'm sure it sounds fine. You don't need to have all cast to benefit, but when you do it is cumulative. If you are looking for addt'l speed and a slight increase in smoothness on top and midrange, consider it, if not then you won't miss it much, especially if you're already digging what you hear. Out of curiousity, what is your pre?