MOTU Digital Performer uniquely handles plugins depending upon whether the plugin GUI is open or closed. When a plugin GUI is open, audio pases through the plugin in real time using the buffer size set in the Audio Preferences. When the plugin window is closed, it uses a fixed buffer length larger than the maximum 1024 samples allowed by Liquid Mix. However, there is an option available in each Digital Performer plugin window which allows for plugins to always run in realtime. Enable this option in all your Liquid Mix plugins, as shown in the screenshot below.
We plan to implement dynamic buffer size allocation in the Liquid Mix in an upcoming release. This will alllow for lower latency in realtime and also higher fixed length buffer sizes for offline processing. See the article at the link below for more info: