Recording Mesa Roadster on Line6 4x12

Hey guys, so I recently grabbed a Mesa Roadster and have started to do some recording with it. I'm having a couple of concerns I was hoping could be addressed.

Yes, I'm using a Line6 cab - it was a more naive time of my life to say the least! Regardless, I'm recording some rhythm tracks, and am finding that there is some pretty noticeable muddiness (or maybe resonance is the right word?) when I'm playing the 9th fret and up.

I'm on the 4th channel Modern setting, 50 watts, and gain is just before 3 o' clock. I'm using a standard 57, as well as a Large Diaphragm EV RE27 N/D, going through an Mbox Pro 2 and Pro Tools 8, and an Epi Les Paul Custom stock.

Basically, what I'm kind of hoping to hear is that getting a better cab would help with the issue (I'm already planning on grabbing a Road King cab), or if this was a common thing to get over, any advice on taming it?

Thanks for the feedback guys!

you could try bringing your head and guitar to a music shop and test out some cabs. Also stock Epiphone pickups aren't the best so an upgrade to your guitar could help tone as well.

Yeah, I am also aware of that to, but one thing at a time! Haha.

Anyone else have any advice or feedback?

First, download the manual for the Roadster because it will be your best source of information. I had it right next to the amp for a few months! Second, and this is in the manual, the more gain you use the less affect the tone controls have, so you probably want them all at or below 12:00. Also, Rectifiers have a lot of low end so you may have to back off the bass more than usual. Third, move your mic back a little bit if you have it right on the grill. Thats what helped me the most.