The peak level will occasionally hit 100% for most movies or music when JRiver's Internal Volume level is also at 100%. There is no such thing as a "good Peak Level reading" when using Internal Volume*. If your volume is turned down, then the maximum peak will also be lower. Music and movies can have content from 0-100% during playback when the volume is at maximum.
If setting any Parametric Equalizer (PEQ) filters, then it is best to make sure you don't exceed a peak level of 100%. You can do this by turning off your amp or receiver, play something in JRiver with the Internal Volume at 100%, and see if your peak levels exceed 100%. If using a receiver, you will probably need to set output to Null Output in Options > Audio > Audio Device in order for playback to work during testing.
*There are exceptions when dealing with other upstream audio gear, but that happens mostly in pro audio settings and isn't really relevant here.