Also, spline modeling is just one technique I would use.  Many of those shapes are just primitives.  I would also impliment hinge from edge, for example, to create the lips on some of those cylinders, and the Loop Tools and set flow tool to create the indents.  Shouldn't take long really, once you get a hang of the workflow in the loop tools.

However, if you want modifiers to work on two objects together, just attach them as subobject elements of the same object.

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