You can send HDMI DSD digital audio to a compatible device from the 105, and yes it can be multi-channel. Set SACD Output DSD.
The Optical and Coax S/PDIF digital audio outputs do not carry DSD digital audio.
As always, when you send digital audio out of the OPPO, the DACs (Digital to Analog Converters) in the OPPO are not involved.
Check whether the Krell offers DSD-Direct-to-Analog conversion for HDMI DSD input. There will be a setting in the Krell to enable that if so. If not, or if not set that way, then the Krell will convert HDMI DSD to LPCM on input before sending LPCM through any audio processing it offers and then to its DACs. In which case, that's the same as having the OPPO do the conversion from DSD to LPCM and sending HDMI LPCM to the Krell. DSD-Direct-to-Analog conversion will mean bypassing any audio processing in the Krell as that processing is done in LPCM.