They are both very nice cartridges.
The Shelter 501 is often referred to as "the poor man's Koetsu".
The Dynavector Karat 17D2 is often referred to as "the poor man's ZYX Fuji.
Not bad company.
Basically, I think the issue is more of a matching condition with your tonearm. The JMW-9 is typically happier with a medium compliance cartridge. I think the Dyna would be a better match than the Shelter, and I think that a ZYX would be a better match than the Dyna.
The JMW-9 is the shortest and least stabilized of all the JMW tonearms. Therefore, it might be wise to not stress it too far with low compliance cartridges, if you want to get best results.
You can't buy a cartridge "in a vacuum". You have to consider the tonearm as an integral part of the package, since they work together as a unit.
