In reply to:
So what's the point of the fancy SPL and DVE and AVIA? Are they perhaps for HT, where the soundtrack mixing is much more consistent?
Speakers vary in their efficiency, even within the Axiom line. Powered subs have even more variation due to the adjustable volume.
While you can also go entirely "by ear", level calibration at least provides a starting point.
In theory with a calibrated system you hear what the mixing engineer intended. IOW if there's little surround it's because he mixed it that way. If there's a lot of bass or little bass it's because he mixed it that way.
With an uncalibrated system maybe you're hearing what the engineer intended, or maybe you're just hearing an artifact of the uncalibrated levels. You never know.
But as you said, there are WIDELY varying recorded levels, esp for bass. Also it does seem more variable for music than HT.
HT is more governed by standards like Digital Dolby, THX, etc. Music is often mixed in a more casual, artistic manner.
Some high res music formats had a turbulent development regarding bass management, and how multichannel should be supported or mixed.
Originally SACD was focused on two channel stereo only. When they finally adopted multichannel, the assumption was each speaker would be full range. Mixing standards and bass management was designed around that. At last the SACD community figured out most customers don't have 5 full range speakers, so began supporting (poorly) LFE/Bass out.
This results in wide variability in bass level across some recorded material.
Another source of variability is the age of original source material. Earlier material was often recorded and mixed assuming the end listener did not have good bass capability. If 95% of your audience is using portable transistor radios, why bother putting in content below 80 Hz?
That's one reason why older content varies so much. Many engineers took the above view. A few far sighted ones realized technology would improve and their music would eventually be played through better hardware, so made the investment in better mixing up front.
Current implementations require WAY too much tweaking, esp if you include the high-res analog input issues requiring double calibration for analog and digital sources.
There ideally should be a protocol developed and calibration info placed on each disc. Similar to the Digital Dolby "dialnorm" feature, except more sophisticated. The receiver could read that, plus read your calibration data from your amp, and adjust speaker/sub levels automatically to meet what the mixing engineer intended (which could vary from disc to disc). You'd have to do just one manual level calibration (none on auto-EQ amps) to provide the initial calibration data.
This would require a digital connection between the high res player and amp, some foresight, better mixing standardization, hardware/software protocols, none of which is currently happening.
