This guy's guide helped me out quite a bit:
http://www.youtube.com/watch?v=1OePkxGXsN0
You'll need to install the same HTC USB Modem driver for both the HTC Diag unknown devices (regular and 9k). If you install them in order, the second COM port will be the 9k one, and that is the port you want to use to connect. I got my SPC (i.e. MSL) using that and wrote the 56013 PRL to my phone successfully. It took a couple tries with the PRL as it always seems to do, but it worked the second time after I turned mobile data off on the phone. Just reboot after writing it, and it should be there.
http://www.youtube.com/watch?v=1OePkxGXsN0
You'll need to install the same HTC USB Modem driver for both the HTC Diag unknown devices (regular and 9k). If you install them in order, the second COM port will be the 9k one, and that is the port you want to use to connect. I got my SPC (i.e. MSL) using that and wrote the 56013 PRL to my phone successfully. It took a couple tries with the PRL as it always seems to do, but it worked the second time after I turned mobile data off on the phone. Just reboot after writing it, and it should be there.