I'm sure you've played with the various tone settings to get more mid and bottom. Also increasing the bandwidth will improve frequency response on the bottom. I'm sure that rig has multiple settings for both. When you are judging its audio quality are you doing it by listening to an RF signal received from a transmitted signal or just an audio monitor?
"If at first you don't succeed, keep on suckin' 'till you do suck seed." Curley Howard, Three Stooges-1936