Graham,

My Bose connects either from the Mono/left 1/4 inch output to quarter inch input on the Bose or from the stereo headphone jack with left and right (red and white) RCAs to input into the Bose. Either way works fine. I'm sure you eliminated this scenario a long time ago but make sure the switch for the Bose inputs is not set for guitar.

God Bless,
Don
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God Bless,
Don