Overall, you may end up this chasing the problem further because when you upgrade the cups you may then start breaking axles etc etc, Check weather the Magnum cups are the same or weather they upgraded them. But yea do the mod and just take your chances with the axles.
Also set up your dogbones with small o rings or slices of fuel tubeing at each end to stop the dogbone putting pressure near the end of the cup and make sure there is no play when dogbone is horizontal.
In all honesty the best thing to do is avoid this truck, sorry CEN but this wasnt your best effort (the MT2) and I like the improvements they did with the Magnum...

If at all possible save up your money and upgrade to a Buggy or Truggy...you will NEVER braek anything like a cup or dogbone...it just wont happen...you spend more on initial purchase but you RC experience will be a lot better (unless its some super crappy brand!! [X(])

Not trying to be smart or anything but I first got into RC with the MT2 and just about know everything there is to know about that truck and it was just a time and money pit (was good learning exp tho) but the best thing I ever did to my MT2 was to put in a .12 single speed and just drive it around the back yard and avoiding anything that resembles punishment!

They are an ok truck but just not quite good enough to be recommended by me.

Sorry if I went on a bit!

And congrats to Cen on the Matrix Truggy, by all accounts its a great truck (from what I have heard, not what I have experienced for myself).