just installed a custom ROM and after that I've installed this MOD. It worked from first time. Now the sounds are a little bit louder, though not to break your ears
many thanks to the creator of this MOD.
HINT: you can use terminal also in order to move those 2 files.
you place the 2 sounds in /sdcard/tmp
go in terminal, hit su in order to have root access and then go in the path where you have dropped the files (in my case /sdcard/tmp)
mv unlock.ogg lock.ogg /system/media/audio/ui
reboot your HTC and enjoy your new louder sounds
All the best!