The equality gate outputs plus when both inputs are the same; otherwise it outputs minus. I initially thought to make this gate using a combination of two monadic 2's (+ - -), two 6's (- + -), and two K's (- - +). These could be arranged such that the gate always produces a - unless both inputs were the same. This would have required 8 comparators since 2's and K's are one comparator each and 6's use two comparators each. Instead, I worked out that, but judicious use of wired AND and wired OR I could build this gate using two P's (which can be implemented with just a couple of diodes), two A's (two comparators each), two 4's (one comparator each), and a single 2 gate (one more comparator). That comes to a total of only 7 comparators. Yay.

The P OR P gate is a Max gate

The A OR A gate (The DAD gate by my naming convention) looks like this

And the 4 OR 4 gate (DD4 gate) looks like this

If you look at these three truth tables and just take the lowest value in each position (through the use of Wired AND) you get this truth table

By passing this through a 2 gate (+ - -) the -'s get turned into +'s and the 0's get turned into -'s and you get this

And thus we have a Equality gate. One that only returns a + when the two inputs are the same and returns a - otherwise. Here is the schematic.