Hey guys, I have the XL for one year and Im still struggeling a lot with harschness. I prefer the Mesa Boogie sound that well known musicians have achieved but me Im fighting these amps (or the axe?) somehow. I did a lot of reading on the forum and the actual amp manuals,
Im using headphones
The problem with headphones is that there is no acoustic reinforcement of the guitar. There is zero coupling between the speakers (inside the headphones) and the guitar. Without that coupling, which is a type of positive feedback, the sound is lifeless, thin and harsh.
When your heroes recorded their guitar parts that weren't using headphones.
On "Appetite for Destruction" Slash recorded his guitar parts in the control room. To get even more coupling into the guitar a combo amp was in the control room with him pointed at the guitar. A volume pedal allowed him to adjust the volume of the combo amp so he could control the coupling. With the volume pedal all the way up he could get controlled feedback.
I've actually done tests comparing the spectrum out of the guitar when there is no coupling (i.e. monitors turned off) and with typical coupling (monitors loud or using a conventional cab). The boost in the low midrange is significant. I forget the actual numbers but it was at least several dB.