As Joth was pointing out, I'm guessing you have 24 loops / valves on your manifold. We just installed 2 manifolds for a total of 18 loops / valves but we are only controlling 5 zones.
But that is not your point, you still need 24 valves, some I'm sure will be hooked together in a bank.
In our existing home I have your basic on/off actuators. They have worked fine for the past 12 years. In our new home that is under construction, I'm going with 24V actuators on/off hooked into a din rail 24 channel DMX controller (the other channels controlling lights and all) as Duncan suggested. I'm sure the PWM actuators from Loxone would be marginally better, but I cannot justify the price in my head as I've been quite happy with the temp control where we are currently.