Well, BMSG seems to have 2 parts to it...
what DY learnt was how to absorb internal energy... what happens as far as I know is that how they practice BMSG is to reverse the flow of how internal energy normally flows, so when they are in contact with their opponents, instead of the energy flowing ---><--- to clash, it goes --->---> into the practitioner's body... and the BMSG that XZ learnt was how to utilise Bei Ming Zhen Qi....
Ling Bo Wei Bu stems from the 8 Trigrams.. which I dun have much knowledge of. But basically, its more of a flow I guess... like how and where to move such that the flow according to the 8 trigrams is followed...