Direct-to-Bus sources allow you to connect an audio input directly to a spatialization bus. Therefore, it bypasses the encoding or panning process of the bus, and goes only through the decoding phase and/or summing.
For all buses except Ambisonics, the bus spatialization parameters (such as spread for example) won't affect the audio coming from the Direct-to-Bus source, as these types of parameters are applied in the panning process.
To assign a Direct-to-Bus stream to a bus, the source needs to have exactly the same quantity of channels as the bus.
In the case of an HOA Bus, choose the Direct-to-Bus channels quantity in correspondance with your bus' HOA Order (and not the Speakers quantity, unlike most busses). You can find the right quantity of channels from the table in the HOA Order section. Make sure to set the match the Normalization setting between your incoming stream and the Bus. Set your incoming streams channel ordering to ACN.
Starting with HOLOPHONIX 1.7.0, Direct-to-Bus sources are not necessary anymore to input an externally encoded HOA Stream to HOLOPHONIX.
Use the HOA Stream sources, that offer better operability and many compatibility options.