What are the condtions for HN2 to connect to a multitimbral setup in a DAW ?

The VSTi must listen to all 16 channels of the "Internal Midi" loopback driver and it must respond to midi program selection messages on each channel.

The device description must contain a collection of sounds with program change numbers assigned. Make sure the soundbank is set to the right "Method of Bank Selection" . Check the MIDI documentation of the VSTi.

HN2 will automatically assign the channels and sounds for you. Nothing to care about once the description is done.

If the sounds are on fixed midi channels, assign those to each sound. You can skip the program selection in that case.