I was able to take out the first Memory Receptacle at Prom-Mea solo as a rng/nin. Key was to stay back and just keep shooting, this way the strays never agroed me. I'd start w/ acid bolts to lower it's defense, used a few, it resists well. Then switched to Holy bolts for most damage. Empty seed would usually only destroy 1 or 2 shadows, but he would recast it fast so had to use bloody bolts occasionally. It was also easier to get hit points back using bloody bolts on a stray when I needed them. The further down the receptacle was, the more it seemed to use Empty Seed. With a whm along it would have been much easier, just have them stay far out of Empty Seed range.
I'm currently exploring second level, hoping to find the ??? and get the map. Will post more as I learn.