I've gone a long way, but have more to do.
1. I purchased 1" thick closed cell black foam with antibacterial and anti-fungal characteristics, with sticky-back. From soundproof.org. I applied it to the four insides of the cabinet, including the doors. It was easy and quick and really lowered the pump vibration noise.
2. I got some isolating pads for the pump to sit on. It is a heavy 3/8 thick pad with grooves in opposite directions on each side. It decouples the vibrations of the pump motor from the floor of the cabinet effectively.
3. Now, other things were noisy! I replaced the hood vent fans (200 cfm) with 220v (40 cfm spec) fans run at 120, to get even quieter. I don't need much air flow.
4. No the halide ballast hum is dominant. I didn't even know it hummed before!
5. Remaining steps. a. Put foam on the ceiling of the cabinet (may not be worthwhile). b.Downscale the cabinet fan. c. Invest in an electronic halide ballast.
Summary, Thanksgiving dinner conversation didn't leave the table for hours, and music from other rooms floated through the dining room, instead of the old roar of our reef!