The way I see it operations like 'MAX' and 'MIN' shouldn't be seen as operations that 'select' a signal, but should rather be ways to reduce many signals into one. The reason this is important is that the game already supports such reduction operations. If you use the special 'Each' signal in the arithmetic combinator, but only output 1 signal then the result is the sum of all signals, and in the decider combinator using the special 'Everything' and 'Anything' signals is the same as performing the operations on 'Each' and then AND/OR-ing the results together.
Rather than making the game more complicated than it already is by adding more combinators it would be a lot neater to simply make these 'reduction' operations explicit. What I imagine this might look like is that when you select 'Each' and output anything other than 'Each', there will be some option to select how the signals are combined. Resulting in something like the following:

Well, obviously the UI could use some work, but the general idea is hopefully clear. The Decider combinator should have (at least) an 'AND' and 'OR' reduction operation, to replace the (odd) 'Anything' and 'Everything' signals, and also a 'COUNT'' and 'SUM' to replace the current behaviour when using the 'Each' signal. The Arithmetic combinator should have at least SUM, MAX and MIN operations.
The one minor problem I see is that in the decider combinator selecting 'output 1' or 'input count' don't really make sense when using 'COUNT' and 'SUM' to calculate a result, but compared to the current behaviour where selecting 'Input count' and '1' may or may not actually ouput the signals input count, or 1, it doesn't seem like a particularly big problem.