VMPS RM30 or RM40. These are super bang-for-the-buck ribbon hybrids that are much more dynamic and amp-friendly than Maggie 3.6s. I believe they are also faster and more detailed.
My previous reference speaker was the InnerSound Eros Mk-II and the VMPS RM30s are more detailed, with better focus and a consideably larger sweet-spot. They sound very close to live music on a good number of my recordings, which is the highest compliment I can offer.
Like any worthy high-resolution speaker they will immediately reveal even the slightest tweaks or changes you make to your system. Yet they maintain their musicality as opposed to other designs that are hyper-analytical but not entirely natural sounding. I'm confident that if you try them you'll find they improve on the performance of the Monolith IIIs in a couple of important areas.
That said, it may take some careful component matching and tweaking to achieve the best results. After all, how long did it take you to optimize the Monolith IIIs? I'm not sure you can plunk any speaker down in a system that was tuned for a different model and expect instant Nirvana. At least it hasn't been my experience.