This is how I calibrated one of my listening setups ( SB3->Cordia Aria->HD 650) for safe max volume levels.
Take 1 Rat Shack Sound Level Meter
Add the Top from a case of Blank CD media - modded without the aid of a dremel.
Put Them together
Now pick a test track from - from the Alan Parsons Sound Check Test CD -
With its quaint warning from before the volume wars.
Reference tones are at the reference level of -14dB.
Warning - This track is at the theoretical maximum recording level, 0dB FS.
THIS IS A VERY LOUD TONE - USE WITH CAUTION
Indeed it is at the theoretical maximum signal level -as if anyone would record at that level in anger - What little they knew what was to come.
Put Them all together and you can set the Max Volume to a Safe 85dB - as seen here.
Result safe, satisfying listening.
Replaygain Tags give you an idea about the signal levels of given tracks and albums so you can compare them to the test signals levels.
Hope you find this useful.