I received my JTV-59 in January 2015. Based on the serial number it was built in late 2014. The guitar was shipped from the line 6 factory directly to my local Guitar Center. I was surprised when I finally got around to checking the guitar's firmware a few days ago that it was v1.9 (the factory siad they would update it to the latest version). So I used Monkey to update to v2.21. Everything went well. And although the acoustic and Lester models were improved, most of the other models were not anywhere near the volume and quality of the earlier firmware. In particular, the Spank model lacked volume and quality. In addition, several of the models had the problem with the low output on the high E and B strings.
I read many posts on the forum on the v1.9 vs HD models. I have experience with Variax guitars as I had a Variax 300 (which I traded in for the JTV-59) so I am not a complete novice. So I rolled back to v1.9 and all the volume and other issues disappeared. I saw that some people have been successful by reinstalling the latest firmware several times. And although I don't understand why this worked I may try it. Also several people set the global string volume to 0 before updating. Again I am not sure why this helps.
As I had no previous experience with the HD models (2.0, etc) I really didn't know what to expect.
I welcome any ideas as to how I can improve the sounds using v2.21.