I haven't checked this thread for awhile (obviously) but I think I have the perfect solution for you. If you don't know about it yet check out Viking Warrior Conditioning. I've been doing it and from what you describe as limits on swings and heavy weight this may be what you need to fill the gap.
In the program you snatch with lighter weight for reps (100's) and it's timed precisely. The program is no joke and takes alot of commitment, but if you want awesome cardio and strength endurance check it out. I started a thread called 'VWC questions' in the kb section of the forum. I'll be happy to help you if you want it