The Brombacher counter is a great weapon for black when decling the Blackmar Diemer. Why ? Not because it is so good, just because it denies white the normal attacking patterns.
The normal line is 1.d4 d5 2.e4 dxe4 3.Nc3 Nf6 4.f3 c5 5.d5 ( Brombacher counter gambit ).
Black's strongest move is now 5...exf3 6.Nxf3 (diagram), transposing into the Kaulich defense.
6...a6 (!?) (diagram) is now recommended by Houdini, but this strange move is not even considered by Christoph Scheerer. It seems to me Houdini wants to avoid some kind of "Gedult variatiation" with Bf4 and Nb5.
How should the attacker proceed ? Let's try some options.
a/ 7.Bf4 can be answered by 7...e7 and white has less than nothing (=+)
b/ 7.Bg5 is probably better than 7.Bf4 but black can chase away the bishop 7...h6 8.Bh4 g5 9.Bf2 Qb6 (=+)
c/ 7.Be3 Nbd7 (=) and white is fighting for equality
d/ 7.Bd3 (=+) gives black the luxury of choices between 7...g6 and 7...e6
e/ 7.Bc4 b5 8.Bd3 (=+) is even worse
f/ The modest 7.Be2 leads nowhere after 7...e6 (=+)
g/ 7.Qd3 runs into 7...b5 (=+)
h/ The waiting 7.a4 (diagram) is maybe best.
The line 7.a4 g6 8.Bc4 Bg7 9.Bf4 00 10.00 seems to give equlaity, but then again, other black seventh moves are possible.
Bottomline, the odd 6...a6 in the Kaulich defense needs to be considered carefully. More investigation is needed, but it seems another oddity 7.a4 is best.