First off your joints need to be replaced. If you are hearing the "marbles" when you turn. You may just had so bad luck. A rock might have tore the new boot. Replacing a CV joint is really just replacing the axle. I have done it before but not in my Subaru. I would rate it a 7 out of 10 on difficulty. Where did you get the boots replaced? I would take it back and tell them that it was faulty.