The cost of plates is higher than more general media, but I might suggest using a chromogenic agar.  A good example is HardyChrom UTI where Enterococcus species grow with a teal color.  They also have an agar that selects for Vancomycin Resistant Enterococcus.  You can find these easily with google searches and Hardy Diagnostics has a good chromogenic media catalog of their products.  Other companies produce chromogenic agars as well.

Ya. Chromogenic agar is readily available as HiCrome Enterococcus faecium Agar Base etc.,

I have used Kanamycin Aesculin Azide agar for the isolation of enterococci from faecal samples and obtained good recovery rates. Try a few different media if you have them at hand. It may be just a case of them not being present. 

It is always better to use azide containing agar rather than using plain bile salt containing agar media. Kanamycin is an added option which might improve the selection better.