X-6 axles will not fit B44 driveshafts. In fact I think if you made the driveshafts go any deeper into the cup they would bottom out when the wheels go all the way up.
Scott- Your best bet is to just get the correct size rear shocks, it sounds like you have XX4 shocks on the back (to long both in the body and the shaft). You need the same shocks as you would run on your X-6 with 2 thin shims to limit the down travel.
