from devilsbook:

I don't know if anyone would be interested in it, but just in case...I had made a hack of SNES9x GX, which is identical to the "official" SNES 9x GX version 004 except that in addition to .zip, it supports other archive formats than .zip, some offering better compression: .gz, .tar.gz, .bz2, .tar.bz2, and JMA, which is similar to 7-Zip (supposedly it gives better compression for SNES ROMs, according to the author of the SNES tool NSRT, which as far as I know is the only JMA archiver).

Credits...JMA code was ported from the desktop version of SNES9x, bzip2 code was based on libbzip2 as included in WiiEngine by Hermes, and gz was provided by zlib, with the tar code by me.

I hope someone may find it useful.