Oooo....you've drawn me out of the woodworks here
. Now I've not heard the 1Plus2 nor Ref 1 for a very long time so I'd actually have to dig out my past notes and past reviews to refresh my thoughts on them and even then, I probably had learnt a lot more and gained more experience in listening to the various other offerings that have popped up in the personal audio market in the past 2-3 years.
So you'll have to take this with a grain of salt.
To me the 1Plus2.2 retains the basic 1Plus2 sound from what I remember. The bass is impactful and tight with a nice reverberating render. The mids to my ears, similar to the original 1Plus2 a slight U shape but not offensively recessed. Texture to vocals in the mids remain beautifully textured, smooth and clear which extends up to the treble region. Now personally for me, and again based on memory, the treble on the new 1Plus2.2s feel smoother and etheareal-ish than the original 1Plus2's. It's almost like the original 1Plus2 took notes from the likes of electrostats and incorporated into the 1Plus2.2's. And from this aspect is where I feel the 1Plus2.2's shine.
One other factor I noticed with the 1Plus2.2 is that it's highly sensitive picking up hiss on setups I didn't notice hiss before. It's made a good tool to sus out setups what a hissy.
Now I'm going to be frank and state that KSE1500's transparency still wins me over the 1Plus2.2 however from the perspective of musicality and ease transportation/on-the-go listening (ever seen the AK380CU+amp+KSE1500 stack!?!?!), the 1Plus2.2 and AK380Cu+amp is an easier daily on-the-go. If I listen to music on my way to and from work, it's the 1Plus2.2+AK380Cu+amp that I use. If I do sit down in a coffee shop for more than 1-2 hrs (which is rare these days with family and kids), then I may whip out the AK380Cu/KSE1500 stack.