I heartily recommend the Korg Opsix to anyone who wants to experiment with FM synthesis.

As the article mentions, the UI of the DX7 made programming it, modifying existing sounds or coming up with new ones entirely, difficult to say the least.

With the Opsix, much of the ability to tweak aspects of the operators, envelopes, LFOs and so on, are given dedicated knobs and sliders, or easily accessible menus whose parameters are tweakable with physical knobs. The hands-on UI of the Opsix turns what once was an ordeal of menu diving and incremental buttons into a much more rewarding, interactive experience.

I play one live in a band and use an old Yamaha KX76, the dedicated controller bigger brother to the DX7 as a controller for the Opsix. Best of both worlds. The feel on those old keyboards is superb.