If you do come to accept a deciduous nature for this project then there is shrubby potentilla, shrub roses and the new Sonic Bloom weigela varieties.

The departure from promised expectation with the azaleas depends on what the specific basis was for claiming USDA 6. With it rather often seeming that plants are listed as being hardy "to" a zone that is really outside of their tolerance range. With this assertion being based on what the top end of the average annual minimum temperature for that zone has been said to be. So for instance maybe the azaleas you bought have been seen to burn up at 0 degrees F. and that became translated into them being "hardy to Zone 6" (average annual minimums 0 to -10 degrees F.)

Just how cold it got at your place last winter would of course be relevant.

We had a couple of frigid days but according to a historical weather calendar, we never dipped below 0F (1 degree F was the lowest recorded). However, we do get strong winds off the Hudson, and these azaleas were in a pretty exposed location (well-mulched but no other protection). The three planted in the spring still have some signs of life, so perhaps getting them in the ground asap plus winter protection would do the trick. Still, they are in a very visible spot in the garden and I don't really love the idea of looking at burlap all winter, so perhaps something hardier would be a better choice.

The Sonic Bloom weigelas are gorgeous - I will definitely consider those!