RME Settings -10dBV +4dBu and low gain

My new RME allows setting the channels that take a 1/4" TRS input with the settings of -10dBV +4dBu or Low Gain.
 
I'm not sure how to pick among them.
 
From the manual...
Level. Sets the reference level of the analog Line inputs. The available settings are -10 dBV, +4 dBu and LoGain.
How do I properly choose among these 3? What are the criteria? Is this only impacting the fader and not the actual level going to Sonar?
 
I understand the Inst setting to enable High Impedance mode for when I plug my guitar straight in, but not the 3 reference levels.
 
When I switch between the reference levels, the signal gets louder or softer... -10 dBV is the loudest, then +4 then LoGain.
 
It seems like these settings are just in addition to gain. Am I right about that? or do they have particular applications.
 
In other words, from my understanding... I would just use the Lo Gain for loud signals and the -10 for quiet ones and +4 for those in the middle. Gain staging before Gain staging if you will. Right?

What Mike said.  those levels match the output of whatever unit you plug into the RME.  So, read the manual of whatever you plug into the RME if it ain't clearly marked on the unit.  Most RCA and 1/4 inch plugs will be -10 dB.  Most XLRs will be +4 (except for mikes).  It just becomes the first stage of gainstaging - a -10 going into a - 10 input should provide the best match between the units as far as noise and headroom.

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