What makes the Bloom around instruments . . .

When an audio product can't separate each individual instrument,singer,or other from each other,that would be the opposite of being articulated.When your system and recording is highly articulated,you should be able to identify everything separately,with it's bloom,and other sonic characteristics,as you would,if listening to it live.I still think someone that isn't familiar with the terms used,would be easiest to compare two products,one that has the quality,against one that lacks it,possibly with someone there to point out where the difference is on the recording.Another way would be to have a recording made by an audiophile with a short cut of music(10 seconds?)with it lacking in it(bloom),against the other that reproduces it good.Without Knowing some of these characteristic's,it could be easily confused with some other descriptive term.At least,that's my two cents worth.I didn't see the Stereophile's full list of them,to see how good they did at trying to make it understandable.

Frogman's description of bloom and the sound of real instruments in a real performance is awesome. Great stuff!!! I'd just like to add that these qualities are rarely present in a studio recording. It does not have to be "live" recording but if the recording is built up instrument by instrument in a conventional studio with all its acoustic treatments, its unlikely to be present. IMO, this is one of the ways that most people can immediately distinguish between a live performance and a reproduction, even when heard from some distance away.

Bloom cannot accurately describe a drum or cymbal's.So it can't be used for all instruments.

I also agree with Frogman's description at the global level. Composer's such as Scriabin and Bruckner reveled in the sonic soup.

Now, here comes the controversial part. While resolving low-level detail is part of it (and I've gone off the deep-end to achieve this), the components are a big piece as well. I say controversial because terms such as neutral and colored are like audio philosophy and religion.

In my experience, if one takes a highly conductive, low gauge wire to transmit power or signal, the result can be sterile, a black background, and an artificial leading edge with truncated decay. For some reason, fine-gauge, multi-stranded conductors of silver, gold, and platinum just sounds real. I will admit that this is altering the signal, but the means justify the ends. Same with tubes, because if you can create a real and intoxicating sound with juicy and dimensional detail, then a system will satisfy on an emotional level.

While trying to nullify weakness by combining different components can be a slippery slope with potential dead ends, combining strengths will open new possibilities.

The XA30.5 had a strong bass and good high frequency extension, BUT, the instrument that was so prominent that it was masking everything else was the drums.

I have never heard an effect like this with the XA30.5. I don't doubt what you are hearing, but I'm wondering if there's some kind of unhappy interaction between the amp and outboard crossovers/speakers that's resulting in a skewed frequency response.

On the other hand, when I think of drums overpowering other parts of a recording, I usually associate that with room modes. But presumably you would hear the same room modes with the Spectron amp, so I don't know what to think. I assume you did not change the position of the speakers when you changed amps.

Bryon