Last year I was starting to lose about 1 qt every 500mi or so. Turned out it was the OFH gasket. Changed that, no more oil loss.
If the engine was burning so much oil as you describe, you would probably have some cats issues by now.

P.S.: that was on my e39 with the same engine you have: M54B30

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Stable: e92is, e46 M54B25, e83 N52, e53 N62 - sold, e39 M54B30 R.I.P.