Its not even that easy, actually; I had to install a while ROM built around it based on CM. I tried just flashing the radio and changing stuff in the Testing options but that didn't do it. It was pretty frustrating but 20+Mbps downloads are worth it ^_^
You can get LTE on the N4 by flashing the 0.33/0.84 hybrid radio at http://forum.xda-developers.com/showthread.php?t=2087227
And enabling LTE through dialer.
I haven't done it because I can't get LTE in my area anyway.
I'm sure sound control will work soon too.
I always used +5 volume boost and never messed with amp gain. What settings do you use?