Also try a few on your midbass. Maybe try one at 310hz and one at ~410hz - both with a Q of 7 or so (both 2nd order). That might take care of those summation issues on the midbass as well.
Allpass filter are awesome when you need them. Some has mentioned that they can cause other issues, but I personally have had nothing but success with them.
If the wide Q=3 allpass filter on the midrange doesn't work well, maybe try two smaller Q ones instead - try to "fix" each dip individually instead of both with a single allpass filter.