You can only store bytes in ROM with DB.

One byte can not represent more than 256 different values. So if you want to store something which exceeds the possibilities of 1 byte; you MUST use more than 1 byte.

The way to create a lookup table with 16 bit words (2 bytes) is to use DW in stead of DB.

You can go as big as you like, but don't expect your assembler to help you do the (assembly time) maths. My assembler (metaLink) can not do more than 16-bit maths.

PS. You are not the first who must hear this: when you use a compiler you are compiling, when you use an assembler you are assembling.