Your engine keeps everyone busy on here...
A head gasket can leak in many different ways, maybe just oil, or just water, or oil to water, some internal only some external only.
So you could have a small leak from an oil way to a cylinder bore without any water issues or any visible signs on the outside.
A compression test would verify integrity of the rings, head gasket and the valve SEATS, but not the valve oil seals.
Valve oil seals are on top of the valve stem, under the valve spring ontop of the head. Not sure of the N54, but it may be a cam out job at most, problem is finding which one of them is at fault!
Do some drive tests with someone following to find out when it smokes, we know Woods are top blokes, so if it is a problem with your recent head work, we know it will be a) an honest failure and b) as gutting to them as it is to you.
E90 330i 6MT gone. E91 335i 6MT gone. AMG E63 Estate gone. M6GC current...