Haven’t heard one yet. It’s a whole new two-box power supply with a large toroidal transformer and a new, bigger AC motor. Impressive! Stereo.net in Germany did a comparison of the model 12a vs MkII and said the MK2 was a massive improvement. An English dealer posted on his blog that the 12MKII sounded better than his original 15.
Comparing the two psu designs which are used across the line, the MKII is FAR superior to the original. There is really no comparison between the two.