New (first) corals, need some advice/opinions

[FitoPharmer]

Depending on what color temperature the 400w bulb was it may have made the corals appear a different color compared to your system. MH can make some colors pop like LED cannot. Normally browning is a sign of too much light or nutirents. If there is little to no change since you acquired the piece my money would be on the MH just made it look nicer. Your montipora digita seems to be very healthy to me with slightly purple polyps. Don't forget to feed your favia for it to grow faster.
As for your question about too much light. Most corals can build up to withstand almost any amount of light, and you have enough light to keep anything in that tank. The real trick is in acclimatization. For more sensitive or bleached pieces you need to start them in the shade on the bottom and slowly move them up. Or with LED's sometimes dimming is an easier option.