Hi Graham,
I've not used the stack function for an LRGB combine for sometime so probably of not much help. Normally I would only use the stack function to combine each of the L,R,G,B sub framed into a master frame. Following this I would use the Colour Combine feature to combine either an RGB or LRGB. I found Colour Combine provides greater flexibility than the Stack combine features. You can read more about it here -
http://www.cyanogen.com/help/maximdl...OMBINETRIC.htm
A word of caution, if the data is already aligned in the stacking process (which it normally would be), then there is no need to align it again with Colour Combine. Avoid realigning data as you risk losing resolution due to additional bicubic resampling the alignment process introduces.
Just as a side note, a straight LRGB combine may sound a good idea but you will probably want to tweak the luminance before it is combined with the RGB data, such as run deconvolution, minor DDP stretch or similar to get the data looking as sharp and detailed as possible. The RGB on the other hand can be of lesser resolution. Here the primary task at hand is to ensure minimal colour noise, gradients and casts. For these reasons, luminance data is typically added to the RGB at a later stage.
