If you want to play on 3.41 you need to install the official Japanese 1.02 Patch [BLJM60273_[UPDATE_01_PS3FW_03.4100]_VER_01.02.pkg], in Multiman (or with FTP) go to /dev_hdd0/game/BLJM60273/USRDIR/SEC, and replace the files there from the original English release. (AG01, AG05, AG10, AG17, AG20 and AG22...)
On 3.55 it should work without the 1.02 Patch, but I haven't tested that, so if you have trouble Install the Patch, replace the files, and Enjoy!
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After installing the game, FTP into your PS3 or access your internal HDD any way you prefer (eg Multiman's file browser)
Go to /dev_hdd0/game/NPUA80636/USRDIR/data/
Move "music" folder to /dev_hdd0/game/NPUA80636/USRDIR/data/gos/
After you done that, you should have 4 folders "dialogs", "movies", "music", "packfiles" inside /dev_hdd0/game/NPUA80636/USRDIR/data/gos/
Have fun playing with epic God of War music
Got it back in mind. You need first a folder with a random number and a total numbers of 8 like 00000428. Then you need to put the pkg into it and you need two Program Debug Database Files (.pdb) such as d0.pdb and d1.pdb, f0.pdb is not needed. You can get those files from your ps3 and edit them or you use the both i have posted or you simply use waninkokos demo manager.
Just edit those both files with a hex editor and change the name of the pkg to the one of yours. Do this on offset 1EF to 1FF and on 265 to 288 on both files. Place it via FTP onto the hdd of your ps3 into the following dir: /dev_hdd0/vsh/task. Install it and have fun.