yeah, if you’re looking an fm with more immediate tweakability than the volca, I think you’re out of luck. FM isn’t really known for that outside of the softsynth domain. The preenfm2 is a beautiful synth, but the menu thing will certainly drive you crazy if you don’t like menus.
if you want tweakability, you can always get a dx7 and one of these:
wow, hadn’t heard of the mmo-3. that looks like just the thing! Damn, I want one of those!