How can I establish a reference level?

With now 350+ hours on my new rear end (I hope it is OK to call the new speakers that, given the common use of the expression front end for the source) I am trying to understand gain and how it relates to listening level. The terms reference level, anchor level, gain structure, dB, dBU, crest factor, etc. all form an ill defined blur. My interest is in protecting one of my five senses. No amount of money and equipment swapping will ever reclaim lost hearing! Now with oodles of distortion free headroom I need to be careful.

Specifically -
JBL 4367 - 94 dB, 300W
Benchmark AHB2 in bridged mono 380W
SONY XA5400ES Compact Disc Player

What I find is -24 dB set on the preamp (with 0 dB being no voltage gain or cut with respect to the source signal) is too loud on most recordings - especially Pop and Jazz. On the 1964 SONY Classical recording of Petrushka, Ormandy (SBK 47664) a gain of -24 dB is pretty realistic as it is on many other classical recordings.
Some recordings sound loud no matter what the volume. Take Jimmy Smith with Kenny Burrell (Phono 870267) for example (listening to him now @ -34 dB)
Much of my listening is far-field, though the speakers are only about 6' apart in an open floor plan of about 1200 sq. feet.

The inverse square law relating to how loudness decreases with distance from the source - how is it affected by a stereo pair? Get on axis near-field with the speakers and just try and keep your mouth shut. Awesome!

So I have a new definition of LOUD and I want to be careful and have some consistency.
I feel -24 dB is a good reference level and am wondering how that relates live sound and the recording process.

The quick answer is that it is very complicated and impractical to calculate the sound pressure level at the listening position based on calculations. You should measure it using a dB meter, this will allow you work out a safe listening level. General advice is that prolonged listening at greater than 70dB SPL could cause damage... this is probably quieter than most of us are used to.
The slightly longer but very generalised answer is that the loudness at the listening position is dictated by the output level of the amplifier, the efficiency of the speaker and the size of the room. The dynamic range of the source material is also a factor in this as heavily compressed recordings will sound louder.
I'd recommend understanding these relationships if you're trying to spec a system to meet your needs i.e. realising you don't need a 300W amp if you have an average sized room and reasonably efficient speakers. But if you want to protect your hearing you won't get close enough to the correct answer without measuring.
Waste of time. For the simple reason every recording is at a little bit different level. Some a lot different. Some compressed real bad. 

But that's the least of it. You're right, your understanding of these terms is a blur. As in, there is none. Pick one or two. Right now I could write a book trying to address all your misconceptions. A page per word at the very least. Seriously. Baby steps. Take one. Which one do you want to work on first?
If you start to feel uneasy it's too loud!
When I read “new rear end”, I thought you were going to say you had a butt lift.😂
I agree that a DB meter is the right tool here.
Your approach is a complicated way to get to a simple answer and will likely not work out. Assuming your primary concern is protecting your ears, first look at what OSHA has adopted for guidelines.
They use science and know. Second, you must understand that while you are listening to music there is a fairly constant change in volume. Maybe some extremely compressed metal music has stretches of fairly constant volume? Third, live music can be much louder than what the OSHA guidelines deem acceptable.

Read the OSHA guidelines, buy a dB meter, play a variety of your favorite music and take some notes about the volume levels (-xxdB) that comply. Repeat as needed. Short peaks are not an issue. Measure at your listening position.

Just sounding (being) uncomfortable or sounding irritating doesn't necessarily mean that you are playing your system too loud. Certain types of distortion are very irritating even at low volumes.
I have pressed the Radio Shack meter into use.
C weighting, slow response.

I set +68 dB up close to one speaker and figure that gives +74 dB of SPL into the room (because there are two speakers and because of room boost).  I hope that this is safe for near-field listening. It seems plenty loud.

As for far-field listening, like when cooking in the kitchen, +88 dB at the speaker seems reasonable.  It is easy to rock the house with higher SPL, but again I want to be careful with my hearing.

No one asked - the input sensitivity on the AHB2 is set to low; 22 dBU (9.8 Vrms).

Empirical results with the RS meter are fine, but I was hoping someone could use the numbers to give me a reasonable idea of loudness from the speakers with respect to the original recording. That would help me gain insight into the process.

+1 @arion, with high volumes being one thing to be aware of when listening, repetitive lower level exposure is cited as a hazard as in industrial settings.
A good HiRez playback System like a Live Music Hall event draw in and demand ones attention.
An enthralling symphony concert can last 2-3 hours at very high levels and extreme peaks without putting anyone in the hospital.
Imagine being in the orchestra playing!
Consider physiological and psychological factors in the evaluation as well.
How your system is integrated into the room can reinforce frequencies in various positions.
Making the system work well is the goal.  
I felt heartened by the OSHA Guidelines. They are pretty liberal or hearing is pretty robust.
Duration of exposure is certainly an issue with home HiFi.
Mike, There really is no direct correlation between the -dB reading on your equipment and the loudness (dB) at your listening position. The levels set during the recording process are all over the map. There are many factors along the audio chain that also affect the final volume.
The audio industry typically measures at one meter as a standard. I suggest that you measure at your listening positions. Room gain varies. The loudness measured at one meter will be considerably louder than at three meters or at your listening position.
The RS meter is robust, durable and pretty accurate- use it as many here have directed.learn to read both the fast and slow for peak and average. Yes the average drives most hearing damage. The OSHA standard may sound conservative but I know and worked w many coworkers who might beg to differ - now.... they may have contributed, but hey we all know better than the scientists....

congrats on your system, enjoy !!!!!