You could try mapping a drive (like M: ) to \\readynas\media then you would just write your files to a subdir off M:\Music.
(you still need to provide a username and password for your networked drive, as explained above. What is probably happening to you is that the NAS is set to allow everyone (even non-logged-in users) to read from the NASdrive, which is why you can see it and the directories it contains) but when you try to write to it it is denied because you are not logged in on your NAS as a valid user who has write access.
mapping a drive in cmd.exe shell (syntax below valid for a Windows-type share)
Code:
NET use m: \\READYNAS\Media * /user:<NASusername> /persistent:yes
Note: instead of * you can put your NAS password for the specified user (if you leave it as * it will ask you for the password)
(depending on your windows version, the /persistent:yes may or may not be a valid option)