Presumably you have seen it, but if not, here’s a link to the manual:
The record outputs may be disconnected (or “defeated”) by pressing the input selector button of the currently selected (to-be-recorded) input a second time. Doing so will toggle the record outputs on and off. The display will alternatively read the name of the chosen input and RECD OFF as shown below.
Defeating the record outputs eliminates even the possibility that the input im- pedance of a recording device could have an effect on the sound quality of the preamplifier. We recommend that record outputs be turned OFF when not in use.