Kerry - I do BFL so I also alternate lower and upper body days w/cardio. I can relate to your struggle. I did legs & glutes extreme last Sunday and was still sore on thurs! I had to push my 2nd LB workout to Sat.
I usually go to the gym and do the Mon step class after lower body. I have also changed my rotation so that on LB weeks I do LB on Sat and then UB on Sun and Cardio on Mon. That way I have an extra day of rest for the legs. It has helped tremendously!
Now I need to figure out how to incorporate the gym style workouts. Today I did both Gym style chest & tri + shoulders, bi and back. W/BFL you're suppose to work the entire UB on one day.
I also just ordered some new dvds on Collage and am going to start incorporating Christi Taylor, Rob Glick and Seasun for some variety. I need some variety in cardio moves as even the HC series seems to be a lot of the same moves and I think my muscles need some variety.
I think my next few weeks will look something like this: (note I do BFL but increase cardio a bit and also have to work in my favorite gym classes which are on Saturdays and Mondays.) Depending on how I feel I usually take a rest day mid-week. I also only do the total body workout on Fridays if it is a week that starts w/UB on Sunday as my UB recovers faster than my LB. If you aren't familiar w/BFL this will probably be confusing - sorry
Sun: UB- Pub or Gym Style
Mon: Cardio- Step at Gym or Imax 2 or 3
Tues: LB- Legs & Glutes, Gym Style or LB workout at gym with added 20 min. on elliptical
Wed: Rest or easy cardio- Lowmax, Christi Taylor hi/lo, kickmax or a cardio segment from CTX
Thurs: UB - PUB or Gym Style
Fri: Total body: Total body workout if I am not doing wts at gym on Sat (bootcamp, high step, circuit etc.) Otherwise I do cardio
Sat: Step interval class at gym
Sun: LB- Legs & Glutes Extreme or Gym Style
Mon: Cardio- Step at gym or Imax 2/3
Tues: UB- PUB or Gym Style
Wed: Cardio- Imax 2 or 3
Thurs:Rest
Fri: Cardio- Imax 2/3 or Lowmax
Sat: Step interval class at gym + LB wts
Hope this helps...
-came back to add that I also like doing the CTX cardio segments as add an as they seem a lot easier after LB days :+