What yogiboy and noromance said. You have a low-output cartridge with a preamp designed for high-output devices. Maybe Grado will agree to exchange. Or you could look at getting a step-up transformer to enable your exiting cartridge and preamp to work together. This is an expensive option.
I used the Dynavectot 10X5 myself and love it. Haven't used the 20X2H but it should work fine. I don't see any problems with a tube preamp.
Good luck!
Gasbose