If my supposition is right you need wide spaced big but soft knobs to handle mud AND roots – a mud spike will slip on roots. A XC winter tyre like the Mud-X is a bit too small and the side knobs aren’t big enough if you want to ride aggressively – on the front that is, it’s fine on the back
What he said…
Mud X’s are brilliant for digging through the mud and finding traction, and they’re more useable elsewhere than a Trailraker, but they’re not very good on roots cos they’re too narrow. You could run then softer as someone suggested, but if I ran a Mud X at less than 45psi I’d ding the rim constantly and I’m only 12 stone. They’re not a big tyre!
Grip over roots is pretty much dependant on having a large volume tyre combined with a soft compound, and knobbles that aren’t too tall or spiky. Something like a Rubber Queen, or even (dare I say it cos I think they’re rubbish elsewhere) a Nevegal, or Minions and High Rollers.
I’m going to be trying a Bontrager XR4 up front and Conti Rubber Queen on the back for a bit, see how I get on, though I expect when the trails turn properly nasty and just getting some drive through the slop is the most important thing, I’ll be reaching for my Mud X’s.