Hi, Jason. The full analog way you are working certainly creates fewer ergonomic and setup problems than with the digital lash ups. The acoustic time delay issue with the drumset is going to occur no matter how you feed foldback to the singer. I’m sorry to say this, but in this case the leakage that is so desirable is working against you in this situation. Instead of isolating the singer I would work on having them sing nearer to the drums to hear them acoustically (say by removing one ear of the headphones) but use a hypercardioid or figure 8 mike as well as gobos to minimize drum leakage into the mike. And not feed the drums to the cans at all.