Just to skip to the summary, the verdict is my mk1 is more open sounding and cleaner than the mk2, esp in the mid bass and vocal departments. Bass quantity and quality largely the same, treble also the same. Granted it isn't fair comparing my mk1 which I have been using since last December, the mk2 is just with a week of use. So I am sure the mk2 will sound better with time but it is quite apparent that the mk2 is not superior sounding right out of the box. I think you might get bigger differences from sample variations than comparing mk1 vs 2.
So hopefully my mk1 will continue to be reliable and will gladly wait for the mk3 to come out.
I've also done a direct comparison of my Mk1 with the new Mk2, and there were some noticeable differences.
I've owned the Mk1 since launch last year, but the unit I have is a third unit I received in replacement a couple of months ago, so it is only burnt in as much.
Overall sound stage and presentation felt similar, but Mk2 felt a little brighter and engaging, compared to Mk1 which is fairly deep and relaxed.
To be honest, I really couldn't say that the Mk2 is a far better improvement over the Mk1. Some may like one over the other but I still preferred the Mk1.
This may simply be my mind justifying my ownership of Mk1, but usually I get excited about new model launches, yet I didn't feel that vibe this time.
One thing that concerned me a little was that the sound (particularly the high-mids) felt uneasy and nervous. Maybe the attempt to get rid of the original Mk1 complaint of too thick and bassy sound has lead to the Mk2 being tuned this way. (maybe it goes away with burn-in but it was quite noticeable).
One funny thing to test is to simply have the left ear with Mk1 and right ear with Mk2, and listen to a monaural track. The difference is quite obvious, though you have to be careful because the two models look identical in appearance so you can never tell them apart visually if they are mixed up.
The character I described above is with using the same cable (the Mk2 cable) on both Mk1 and Mk2. I also tried my ALO Tinsel but felt the same tendencies.
The new cable felt better than the old Mk1 cable. It does avoid the bass boom and generally keep the sound tight. I still prefer using my ALO Tinsel since it gives a clearer presentation, though it does sound restrictive in dynamics at times. I think the Mk2 cable is a good all-round compromise solution.
Anyhow, I didn't feel an urgent need to chuck out my Mk1 and replace it with the Mk2... thankfully.