There are two additional dumbbell variations you can try which will keep your lower back and chest supported and allow you to use two dumbbells in each hand at the same time. (fitnessandpower.com)
Unlike single - joint dumbbell variations, cable crossovers and flies, including those performed on the peck deck machine, allow you to flex your pecs in the top contracted position on every set, thereby working the chest hardest in the full contracted position and calling for a greater involvement of the inner pec fibers. (fitnessandpower.com)
Incline Barbell, Flat Barbell, Floor Presses, Lock Outs, and every other Dumbbell variation under the sun were my only concern. (onnit.com)