How can I establish a reference level?

Update:

In house now is a ML No. 534. OMG!!!

This amp and speaker combo effortlessly produces the whole thing.

Like a tapestry.

Noticeable are the dynamics. Quiet and LOUD! 

The JBL 4367 and ML No. 534 play exceptionally well together.

UPDATE:

Having not had any parties on my porch for some time, I have switched back to the XA-25 in front of the JBL 4367. I'm glad I did. The 94dB JBLs get as loud as I want with the XA-25 and sound absolutely fantastic. The higher powered amps, ML534 and Benchmark AHB2, seem to prefer higher volumes and this is tiring. On the JBL 4367 the XA-25 gives me fatigue free listening and sounds more like music at all volumes.

Noticeable are the mid-bass textures and overall glare-free presentation. Those 15" woofers are handled with aplomb by the XA-25. It is amazing that 25W will do it, but these are a very special 25W. To paraphrase Dick Olsher, if the first watt is no good who wants the rest?

UPDATE:

It is time for a correction. After playing around for a while with the low power amps I have come to the conclusion that they do not sound "more like music at all volumes." Instead each puts its own spin on the sound and gets to sound less like music at higher volumes.

Switching back to the Harmon duo, specifically the ML 534 paired with the JBL4367, noticeable are the MACRO dynamics and KICK. Back is the house filling sound!

So, if you don't feel too silly sitting near-field to these speakers the lower powered amps are fun... Unfortunately though, the first glorious watt (or 40 watts) may ultimately not be enough for the 4367.

I forgot to mention,

Also noticeable with the change is the HUGE soundstage. With the right recordings I am immersed in a sound field that extendsr beyond the boundaries of the room. Be it Alan Lomax "Southern Journey" or Barbie "The Album" the effect is of being surrounded by sound.

UPDATE:

I’ve finally established a reference level for playback in my listening room. It took yet another new amp with an interesting property. A friend recently commented, "It sounds the same when you turn it down." Think about that. Opposed to the low power amps which sound better when you turn them down, and the high power amps which sound better when you turn them up, you get the same quality of sound at all levels. This obviously makes it easier.

The other thing is I prefer the 2 Ohm tap and I’ll tell you why in a minute.

Have you guessed it yet? (I’m the slime oozing out of your TV set) - sorry.

It’s a MC462.

I have been listening to the new amp for the past 2 months and on one recording the difference between the 2 and 4 Ohm taps is readily apparent; on the 4 Ohm tap the classical guitar sounds compressed and the violin sounds way too good to be true. (Hadelich/Villegas "Histoire du Tango").

Using the 2 Ohm tap, the amp is the most honest I have heard. I could speculate why, but why bother? (Do note that I mentioned the VARIAC earlier in the thread.) And no, I am not using the VARIAC with this amp.

An added bonus is that it warms up and is ready to play in the time it takes to brush your teeth.

I love it!