The CPU Monitor shows you how much processing power each machine consumes. It also shows WM Errors, which are generated when a machine is generating silence but for some reason didn't switch off completly.
T/SeqT: Is the time used for the parallel processing divided by the time the processing would have taken sequentially. So if it's not below 100%, the processing is actually taking more time because of the multithreading overhead. In practice you probably need two or more generators that use 5% or so each for multithreading to be useful. And even then it's better to use just one thread if it's enough to play your song.