Strength train and add conditioning
Depending on how strong you are and how heavy the strength-endurance exercises are, the best option for improving your strength-endurance may be to continue getting strong while doing some token conditioning work. This might mean sprints, barbell complexes, Prowler pushes or whatever on off-days or at the end of the workout. If your recovery suffers by adding this extra work, you may need to subtract some work from your lifting routine, for instance, by separating your lifting into A and B days. One random stab at that kind of set-up could be:
A Day: Squats, Dumbbell bench press, wide grip rows, dips (with added weight), clean and press, 10 minute barbell complex without rest
Deadlifts, shoulder press, pull ups, dumbbell bicep curls, narrow grip row, maximum number of kettlebell snatches or clean-and-jerks or swings in 10 minutes
If you consider yourself strong, then adding some conditioning is called for at the end of every workout. If you still have a ways to go before considering yourself strong, then maybe you should add one conditioning exercise per week.
Reduce strength training in favor of extensive conditioning
Conditioning is highly activity-specific. If you want to be good at the 300 workout, do the 300 workout. If you want to be a good runner, then run; to be good at swimming, swim, and so on. Maintaining a variety of conditioning exercises, such as is done in Max Effort Black Box type programs, is a good way to get good at strength-endurance across a broad spectrum of possible tasks. This would involve a more dramatic reduction in the amount of strength-specific work, however, since these programs are generally geared towards someone with an acceptable level of strength. They are often programmed with only a single strength movement for each workout, followed by conditioning/strength-endurance work.
Set clear goals
It's important to be clear with yourself about the short list of things you want to improve with your current program. Trying a new workout and getting a novice's exhaustion from it does not necessarily mean you have to add it to your routine--it just means that there are many areas of physicality, most of us can't do all of them well at the same time, and strength-endurance or conditioning workouts are specifically designed to make anyone tired. If you chase every workout program that makes you tired, you'll be unable to make progress.
