Those manuals are full of helpful info about the odd ways certain makes and models behave. From Yorkville's xm200 manual:
XLR Line/DI Output
Line/D.I. Selector Button
The D.I. / Line selector switch enables you to configure the behavior of the Line/DI Output.
In the D.I. setting, the button connects the Line/DI Output directly to the Input section thus bypassing theVolume control, Tone controls and Effects Send/Return circuitry. You would use the D.I.setting in a recording or P.A. situation where the mixing technician requires a completely dry signal, as ifit were a DI box, Direct from the Instrument.
In the Line setting, the button connects the Line/DI Output to the final preamp stage so that the Volume control, Tone controls and any connected effects all affect the signal. You would use the Line setting when connecting the Line/DI output to the input of another amp perhaps for added stage coverage, or to a recording or P.A. mixer where a dry signal is not required.
Tip: For most club PA situations, or for home recording, you would probably prefer the Line setting.