Oh, I’ve just found out a nasty thing about the installer. It won’t install on a non-Japanese OS even with the code page trick.
You will need to run it, copy the temp files out before the installer deletes them (once you see the error message), and then modify the SetupSS.ini file.
Change supportoslang=Japanese to [supportoslang=English and it should work.
[Initialize]
fontname =FONT_NAME
applicationname =APPLICATION_NAME
supportos =0x78
language =Japanese
supportoslang =English
nonsupportoslang =
schineseopt =1
mainsection =SdWelcome
dlmanager =1
dlserver =http://www.aii.co.jp/contents/smojsdmk/p-audio/sonicstage_3000/
noaskopt =0
instssver =3.0
uninstomgver =2.2
pacsupport =