While DB can be substituted for KB, it's not the same. I struggle with this when I do KB workouts with DB at the gym. There's no stability required when using DB for swings and they're awkward if you're trying to do cleans or snatches.
Same thing with Sand Bag Get Ups. I don't know how you got it to work for you
CDG but it was a pain in the dick using DB for SBGU. I usually stuffed as much shit in my sea bag as I could and used that.
Overall, I've been able to tweak or substitute things here and there and make MA work for me. I could nitpick any system to death, but if you want to make it work, you'll find a way.
Someone pointed out the KISS method in another thread I think. Swim, run, do push ups, sit ups and pull ups. Throw in some moderate weight lifting and you'll be GTG. When the dust clears, you'll be relying on the little muscle that takes up the 6" between your ears more than anything else.
ETA: I think MA is a great program and they have selection based options now. I never used SEAL Fit because I was too lazy to look up all the fucking exercises that I didn't recognize...usually about 75% of their WOD.