i emailed theta and got a very prompt response from their technician carl (impressive). he told me to check the manual and search for Analog Direct Mode... so i did precisely that and here's what i found...
"Analog Direct: this mode takes the selected analog input and routes it directly to the main Left/Right outputs via the volume controls. Since there is no surround processing in Analog Direct, the sub woofer, EQ, phantom center channel, and crossover effects are not available. Note: If these effects are desired, use the STEREO mode. The Analog Direct mode will route only an analog signal to the outputs.
Analog Matrix: The signal routing in this mode is the same as Analog Direct, left and right analog input signals routed directly to the main outputs via the volume controls, and at the same time, the input left and right signals are routed through an analog to digital converter in order to derive the other channels, which include left and right surround, sides, center, and center surround. These other channels can have EQ and be crossed over (creating a SUB channel), but the front left and right channels may not have EQ, be crossed over (routed to the sub woofers), or perform phantom center speaker. The Analog Matrix mode processes an analog input signal only."
so, seemingly one can input an analogue signal to the CBII and bypass the internal DACs with some limitations.