I don't think I could ever get rid of my 5150 Sig. head, Orange 4x12 and analogue pedalboard unless I absolutely had to..
That rig is like my trophy, I spent close to 10 years saving money, trading gear, gigging, meeting people..etc. to finally acquire that rig..
Even though my Axe Fx blows it out of the water..I'd still feel terrible selling it.
That's one fo the problems I'm having.
When I was a young budding guitarist, I spent a lot of time envisioning exactly what I wanted out of my rig. The tones, the options....I would even spend hours photoshopping a visual guide of what I wanted, just to further the power of thinking so to speak.
I spent a lot of time finding the best deals I could (got my Mesa 4x12 in mint condition for $350, the Mark IV Rackmount for $970, Axess FX1 for $700 which at the time was stellar). Fast forward some odd years, and I got the exact rig I'd been envisioning for so long. Weeks and months programming and tinkering to make everything perfect, both in sound and working...and then, enter the Axe-FX...haha.
So yeah, the Axe-FX does everything my rig does and then some, with less trouble and weight. At this point it's pure sentiment and ego that's holding my back from selling my rig. It's kind of sad in a way, lol.
My rigs are too cool and sentimental for me to sell, even after having the Axe-Fx for over seven years. Mesa/Boogie Mark IV narrow body combo (same issue as the original poster with the sound changing/fading... probably needs a retube), TriAxis (also needs repair), Quad, Mesa 4x12, SansAmp PSA-1, and other amps and stuff all lined up on a wall of G.A.S.
Maybe I should replace them with a bunch of cardboard painted to look like a wall of 4x12's...
Just a heads up. I spoke to Maddi (John Petrucci's guitar tech)a while back about the issue I was having. He spoke to a couple of his connections at Mesa for me, and they told him that it COULD be a tube issue, but that the Mark IV was such a complicated amp, that it could easily been one of a dozen other things. Whereas with most amps the tubes are generally the problem, apparently the Mark IV could be a whole different issue.
Needless to say, with lack of expendable income and the Axe-FX at my disposal, I haven't taken my Mark IV to the shop like a good owner should (because I have a truck that gets 12MPG and the nearest authorized boogie repair store is over an hour away). I still have no idea what causes my issue.