If the fixed cup keeps giving you grief, try this approach: Put the rest of the bottom bracket back on the bike and put the fixed cup wrench over the spindle. Get yourself a good sized sturdy washer with an outer diameter larger than the wrench and the center that will fit just over the spindle. Get a short section of sturdy pipe with an inner diameter a little bit bigger than the spindle diameter and outer diameter big enough not to slip through the inside of the large washer. The pipe length needs to be long enough to take up the distance of the spindle. Top it off with a washer larger than the pipe. Thread on the spindle nut or bolt to snug everything up, pressing the fixed cup wrench firming onto the flats. That should help give you leverage to crack the cup free without the worry of the wrench slipping off the flats. I probably didn't do a very good job explaining it, but hopefully you can get the picture.