I am assuming the JH's are customs, right? That's impressive given the fact that the JHs have 4 drivers dedicated to bass alone.
I am not impressed at all with driver count, and thats seems to be the trend. Every driver is a failure liability. I much prefer Shure's philosophy on the matter - instead of hosing the problem down with more drivers, simply get more from the drivers you DO have.
True JH15 has 4 drivers for bass, 2 for meds and 2 for treble. Yes that makes the 846 pretty special having only 4 but the 846 is a newer model with improvements and a new design for the bass. Both are great earphones that can make any style of music shine. I like customs but when I am off to work I usually grab the earphone I can put on and remove while on the go and it is usually a universal.