Rules of Hierarchy

The way to refer to another schematic as a block in a higher level schematic is to create a symbol with the same name as the block schematic and then by placing that symbol on the higher level schematic. For example, if you have a top-level schematic called topXYZ.asc and another schematic file called preamp.asc that you wish to place in the schematic of topXYZ then create a symbol called preamp.asy and place an instance of that symbol on the schematic of topXYZ. The electrical connectivity between the schematics is established by connecting wires of the higher-level schematic to pins on the lower level block's symbol that matches the name of a node in the lower-level schematic. As the names of symbols used as schematic blocks and the names of the schematics corresponding to those block must consist of valid characters that can be used as filenames. They also cannot contain the space character.

LTspice will look in the directory of the top-level schematic for symbols and blocks to complete the circuitry of the top-level schematic.

The symbol you create to represent the lower-level schematic block should have no attributes defined.