Peter, can you tell me a little about your painting process? Are you spraying or brushing? I'm assuming you are using Urethane.
Patrick, I'd always spray unless I was going for some effect with brush, and yes, two stage urethanes would be my weapon of choice.
On MDF, urethane high build primer, then sand 220. Fill and sand, probably one more coat of primer, sand to 320 or 380. Spray color, then two coats of clear. Wet sand 600 or 800, two more clear, wet sand to 1200 or 1500. Power compound and polish.
I don't have a paint booth so the last cut and buff is necessary to get piano finish. Ruben gets some killer finishes, and has what appears to be a really nice booth.
FWIW, Wood cabinets with lacquer are easier to get looking good, the glossy paint finishes are tougher.