Your PSR 620 sshould be able to read a file from disk in .Mid format without any conversion. I download files to disk for my 730 all the time. Make sure you are actually saving them as .Mid files, and not HTML files. on some sights, you have to open the file then save it. Just right clicking on the file name often saves the target as a HTML file, that cannot be read by your keyboard. You can also format a blank disc in your keyboard, and then insert it in your computer... formating the disc on the keyboard adds 2 files that your keyboard uses when it plays back files. I have not found it to be essential though. Hope this helps,
Dave Waldman