Q: Why is some of my Apollo's DSP used when I have no UAD plug-ins loaded and no DAW open?
A: Apollo's internal mixer engine - which makes Apollo’s features such as Realtime UAD Processing and routing possible - inherently uses a small amount of the Apollo's DSP/MEM resources. The DSP usage of the internal mixer engine varies depending on sample rate and what features are currently being used in Console - for example, the idle DSP usage of an Apollo running at 96kHz will be higher than the idle DSP usage on an Apollo running at 44.1kHz. Because of this, it is entirely normal to see a percentage of your Apollo's DSP/MEM being used when there are no UAD plug-ins loaded and no DAW open.
Depending on how you are using your Apollo you may be able to reduce the idle DSP usage by tuning certain features in the Console application, as well as by working at a lower sample rate if possible. One example is the "Input Delay Compensation" feature in Console. This feature is used to keep multiple inputs phase aligned when using internally upsampled UAD plug-ins in Console, and also makes sure that the correct delay amount is reported to the DAW so that audio is placed correctly into the DAWs timeline. Disabling this feature when not needed will conserve a small amount of DSP. To disable, open Console, navigate to Settings > Hardware and select "Off" from the Internal Delay Compensation menu.