Well, I have some experience w/ HID systems. If you won't be using the lights at the same time, I would suggest going with a switchable ballast, that way you can use MH bulbs and HPS bulbs on the same ballast. Alternatively, you could buy an HPS system and shell out the extra $50 for a MH conversion bulb, and you could use that on the HPS ballast. If you plan on using them both at the same time, you're going to have to buy 2 ballasts, 2 reflectors, etc... You want a reflector that mounts the bulb horizontally, rather than vertically, as they are more efficient. By far, the best reflector I've ever seen has a double parabola shape, and goes by the brand name Adjust-A-Wing. PM me for a source if you want it. Lumatek makes good ballasts, and Sunburst too. Digital ballasts are supposed to be quieter and more energy efficient than the typical core and coil ballast. I've never used a digital ballast, so don't hold me to it. If you have any other questions, feel free to pm me...