You could place as many "x" inputs for "1" output and vice versa.

How to use:

Underground Belt:

• First Input: Put one Underground Belt Input, and then the Output.
• First Output: Put one Underground Belt Output, and then the Input.

Underground Splitter:

• Put All Outputs you want first. Then the input.

Underground Merger:

• Put All Inputs you want first. Then the output.

Video:

Icon /UIs and Graphic Advices by Deantendo#4265 - https://discordapp.com/channels/555424930502541343/701160102077530213