For me, kickboxing is the easiest to keep low impact and still keep my heart rate up. You said you have all of Cathe's... maybe try Kelly Coffey-Meyer or Tracey Staehle. I know Amy Bento also has a bunch of kickbox-ish workouts but I haven't purchased them because the clips look like a mix of hi-lo and KB and too much high impact for me to modify. Maybe someone who has some of hers can confirm or deny this.
You can always get some walking DVDs like Leslie Sansone but they definitely do not qualify as high intensity. But there are times when they are just what I need.
hope this is helpful.