After some experimentation and mental gymnastics, I think I've landed on a way to incorporate both P90X and Insanity workouts in a balanced, 90-day program. Here's the schedule I'm going to try to follow:
Weeks 1, 3 and 5
Day 1: P90X Chest & Back, Ab Ripper X
Day 2: Insanity Plyometric Cardio Circuit
Day 3: P90X Shoulders & Arms, Ab Ripper X
Day 4: Insanity Cardio Power & Resistance
Day 5: P90X Legs & Back, Ab Ripper X
Day 6: Insanity Cardio Recovery or P90X X Stretch
Day 7: Insanity Pure Cardio and Cardio Abs
Weeks 2, 4 and 6
Day 1: P90X Chest, Shoulders & Triceps, Ab Ripper X
Day 2: Insanity Plyometric Cardio Circuit
Day 3: P90X Back & Biceps, Ab Ripper X
Day 4: Insanity Cardio Power & Resistance
Day 5: P90X Core Synergistics
Day 6: Insanity Cardio Recovery or P90X Yoga X
Day 7: Insanity Pure Cardio and Cardio Abs
Week 7 (Recovery Week)
Day 1: Insanity Core Cardio & Balance
Day 2: P90X Yoga X
Day 3: Insanity Core Cardio & Balance
Day 4: P90X Yoga X or X Stretch
Day 5: Insanity Core Cardio & Balance
Day 6: P90X X Stretch or Core Synergistics
Day 7: Insanity Core Cardio & Balance
Weeks 8, 10 and 12
Day 1: P90X Chest & Back, Ab Ripper X
Day 2: Insanity Max Interval Circuit
Day 3: P90X Shoulders & Arms, Ab Ripper X
Day 4: Insanity Max Interval Plyo
Day 5: 100 Pull-Ups and P90X Ab Ripper X
Day 6: Insanity Max Recovery or P90X X Stretch
Day 7: Insanity Max Cardio Conditioning and Cardio Abs
Weeks 9, 11 and 13
Day 1: P90X Chest, Shoulders & Triceps, Ab Ripper X
Day 2: Insanity Max Interval Circuit
Day 3: P90X Back & Biceps, Ab Ripper X
Day 4: Insanity Max Interval Plyo
Day 5: 100 Pull-Ups and P90X Ab Ripper X
Day 6: Insanity Max Recovery or P90X X Stretch
Day 7: Insanity Max Cardio Conditioning and Cardio Abs