It turns out I'd missed the part of the KEF 107/2 manual that deals with biamping. Obviously KEF anticipated that 107/2s might be biamped and provides a schematic for it, using one stereo amp for LF (both speakers) and the other for MF/HF (both speakers). I've seen this called horizontal biamping, in contrast to vertical biamping in which one stereo amp drives both the LF and MF/HF of a single speaker.
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