$140 for the custom threaded feet. A bit steep, but not bad considering the amp is 4k new. :D
It'll have to wait a bit though as I just dropped 300 at Record Store Day.
No doubt Mapleshade feet would do a fine job controlling vibration and look much better cosmetically than my setup and even better than a stock CS300XS. Just be sure the Leben is placed on a sturdy rack or platform and you would be good to go MT. Only problem is, and I know this from doing business with them, their products are not exactly inexpensive.