It depends on what you mean by a closed loop. Since you mentioned a control application, I'm guessing you want to perform point by point control and are attracted to the 4461 since it has 24 bit inputs and outputs. If this is the case, the 4461 isn't ideal since it was designed to acquire dynamic signals. It has very good dynamic range and THD characteristics, but it doesn't have great DC accuracy. The board only supports waveform acquisition and generation, and it doesn't support single point measurements. Also, the digital input filters on the front end will delay the input anywhere from 33 - 62 samples (based on front end configuration) and the interpolation filters on the output will add another 32 - 48 samples of delay (depending on the sample rate chosen). This creates a minimum total delay of 65 - 110 samples worth of time before a real word signal can be measured, processed, and output to the real world again. All of this makes the choice of the 4461 non-ideal for point by point control unless the control loop rate is relatively low (maybe 1 kHz, probably a couple hundred Hz).
On the other hand, if you're looking to acquire a block of data, process the block, and change an output waveform accordingly, the 4461 might be what you're looking for. Without knowing more about your application requirements, it's hard to say.
