I don't understand why are you folks running the threshold so high? My typical settings are sensitivity 8, threshold 3-5, 2 or 8 tones depending on where I am hunting, volume 75-85, either no bars discriminated out or in trashy areas just the lowest 3 notched out. You want to set the threshold as low as you can go and still hear it. Even with these settings I have to turn the volume on my White's Pro Star headphones down 3 to 4 clicks from maximum so they don't blow my ears off on shallow large targets. If I crank the threshold up into the twenties, it will be chatty as all get out. With that said, the MX5 and MXT will never have as smooth sounding threshold as the Minelabs. Try dropping the threshold down below 10 and crank the volume up. I believe even the manual states set threshold as low as you can and still hear it.
Good luck,
Matt