Well the M-One XL arrived yesterday.  It does indeed sound very nice.  However, I do have a problem.  There appears to be an impedence mismatch in that it doesn't work properly in the effects loop of the F-1X.  Thus, in the chain, it's sitting between the F-1X and the power amp.  I still have a lot of work to do dialing in a good overall sound; but fortunately it's an enjoyable exercise.