What setting should my amp’s input sensitivity switch be set at?

I am hoping someone can help as I am not an engineering type. I have an integrated Vitus amp connected to a CD player via an rca cable. The amp has a sensitivity Vrms setting for each input. It has three settings <2, <4, and <8 vrms. Would anyone know what this should be set at? The lower the setting the louder it goes but I am sure there is more to it than that.

Thanks for any advice you can give.
A CDP has an output of 2 volts which is enough to drive your amp. If you find it is too loud just change the setting on the amp to a higher setting to lower the volume. That is a nice feature on that amp!
don vito is right. Leave the gun, take the canoli. Er, I mean use the one that sounds right.

The non-technical way to think of this is, you know how sometimes you have to turn the volume up (or down) a lot when going from one source to another? Vitus is simply giving you a way to make them more the same volume. Its a convenience feature.
Generally a CD player is supposed to be 2 volts (with an RCA interconnect) (With a XLR that would be 4 volts) . But many are more. The way to find the right setting is play music. adjust the volume to HALFWAY. if it is too loud at V 4 setting, move it to 8. If it is too soft at 4v try 2v  
The 4v -8v is for XLR balanced. The 2V / 4v would be for the RCA, unbalanced)
also the Vitus may depend on it NOT OVERLOADING the input. If you set the ’v’ too low, (so the integrated makes it really loud at a low volume knob or control setting).. you may be overloading the input. (If that is hard to understand ,do not worry about it.) So you might want to start with the 4v setting and see where the volume control IS with the CD player input set to 4v.
Play Rock music, as it is mostly loud on the CD. Where Classical and Jazz may be only moderately loud. You want to listen to music which is using most of the CD loudness.
Most equipment is happy playing at 50% to 60%... Give you lots of room to play softer, or louder. I looked up a Vitus not knowing your model, and the Vitus I looked at has balanced inputs and RCA. So again I would start with the 4v and see how close the volume knob or control is to half way for pleasing level of playing Rock music with either RCA type or XLR type cables.
You're welcome ! Hope it helped.