The processing delay for each output is given into the menu SETUP / SOUND PROCESSING.
This delay is non audible: even into the 4-band version, it is typically under 6ms.
Can factory presets be modified and overwritten causing lost of preset?
No. With Digiplexer 2/4 you will never lose any preset:
Factory presets are always available from the menu NEW PRESET
User presets that has been saved are automatically logged. You can for example restore a very old preset you liked before.