Hi Chris,
My experience is the same as yours. There is definitely something lacking in the sound. Although it is more ‘involving’ and grabs your attention, it is also less ‘involving’ in the sense that it doesn’t draw me into the music and make me feel lost in it. There isn’t the same emotional connection. Hard to describe, perhaps it sounds more ‘digital’ and less organic/real.
In terms of reverting back to the previous firmware, I believe this is possible (thank God!!!) as confirmed by Stevesky - as below: