A good rule of thumb is to try and achieve the desired level as early in the chain as possible, as adding gain later in the chain will amplify any noise coming from the earlier stages. The +4 setting on both the inputs/outputs is ideal if your devices before/after can handle it. If not (as you say, if your source can't push the meters past the middle), then it might be better to use -10 on the inputs as this will keep you from having to use make-up gain later on down the line.
