Hi
I also have knee issues. I've had arthoscopies on both my knees, which have not been due to exercise. I twisted them whilst dog walking lol. I find some plyo moves okay. Such as jacks and high knees. However, I do have problems with the RWH Cardio as I can't jump on the higher step and also hopping on one leg at a time is just too painful for me. I just try and do what I can. I think also its working with what you have and doing the things you can.
Also I have recently thought about attending a gym so I can have access to heavier weights. I do think heavy weight is needed to increase strength in the legs (or anywhere else). I am restricted as I have only limited weights. I went to a local gym and tried to do squats with an olympic barbell, but because the barbell was much larger than I was used to I had real issues keeping my balance whilst squatting. Strange, but I could only do the squat movement with an unloaded olympic barbell. Not very good for strength gains lol.
Laura