Wolf,
If your issue really extends up into the octave below middle c (when you said below middle c, you didn't specify how far below), then I doubt that the sub is the answer.
In my case, the issues were more centralized in/below the lowest full octave on the keyboard. One idea:
Make sure you've tried your existing set-up in several different environments before concluding that you've nailed the specific characteristics of the problem. In this frequency range, the room is (almost) everything.
Good Luck,
Marty
If your issue really extends up into the octave below middle c (when you said below middle c, you didn't specify how far below), then I doubt that the sub is the answer.
In my case, the issues were more centralized in/below the lowest full octave on the keyboard. One idea:
Make sure you've tried your existing set-up in several different environments before concluding that you've nailed the specific characteristics of the problem. In this frequency range, the room is (almost) everything.
Good Luck,
Marty