When setting preamp for Dyna 10X5, I was going with 1k load. You will probably have enough gain, but 100 ohm load may give you a "muffled" sound. However, as the preamp works well with your MM carts, I wonder if somebody returned it to the default state (47k load). In that case sound will be on the bright side but, depending on the rest of your system, it may sound just right. In any event, once you get the new cartridge and if you are not satisfied, it will not be difficult to optimize the preamp for it.