the problems you have are normal, and can't really be fixed because of how it works. this plugin here is no longer relevant mostly because of that, and since a much better method was found.
it doesn't require you to install soundforge which stops working after 30 days or so, and plays the decoded sound files through the emulator itself rather than additional program in the background, so there shouldn't be any delays or mistakes.
http://www.emunewz.net/forum/showthread.php?tid=129065
also use the newest emulator version off the buildbot, the support for external decoding of the at3+ sound using the new decoder was added not too long ago, as well as fixed to play at the right pitch.
http://buildbot.orphis.net/jpcsp/index.php
it doesn't require you to install soundforge which stops working after 30 days or so, and plays the decoded sound files through the emulator itself rather than additional program in the background, so there shouldn't be any delays or mistakes.
http://www.emunewz.net/forum/showthread.php?tid=129065
also use the newest emulator version off the buildbot, the support for external decoding of the at3+ sound using the new decoder was added not too long ago, as well as fixed to play at the right pitch.
http://buildbot.orphis.net/jpcsp/index.php