well, you can start wherever you like i suppose... you can calibrate, register and stack in PI as well.
if you want to do LRGB i guess i'd bring in the L and R/G/B images as greyscale images, then do DBE on each separately (this affords you a little more control than doing DBE on a RGB image), then merge the RGB using either ChannelCombination or PixelMath, then work on L and RGB separately and finally replace the implicit L in the RGB image with the main L image, using LRGBCombination. you do this by only selecting an L image in the LRGBCombination dialog, setting up the transfer functions (i usually make the saturation slider somewhere between 0.3 and 0.5, which will boost the color) and applying the LRGBCombination process to the RGB image.
you can actually also do the R,G,B -> RGB image combine with LRGBCombination if you leave out the L image and leave all the other settings as defaults.
rob
