[pixxel]

Just for you to know, don't ever edit your firmware files with notepad. You should use either specialized hex editor, or find z80 IDE, and look the assembler code within it. The problem is, that text files consist of the first 128 bytes (out of 256) in the character table. As soon as notepad finds other characters (which are there as this is assembler code), it converts whole 'text' in Unicode, thus changing the code and destroying it. Thank god you had backup, and always keep it in a safe place...
If you want to change your firmware, you should do this:
1. Use s1fwx to extract files from the firmware (there are several good tutorials here)
2. Find which file you want to edit
3. Use z80 IDE and
a) Hex-edit what you need, or
b) Edit assembler code directly (if you know z80 instruction set, and hardware specifics of your player)

As you can see, without knowing WHICH file does equalization, and knowing WHICH address in assembler calls volume controlling hardware, it is nearly impossible to do any of this stuff. Our players are Chinese, are made, well, not really made, more like they're bundles of all parts together... They surely don't have a hardware specification, or technical sheets...
And if you are thinking of editing images only, there is a post below which explains it pretty good...