I thought following interpretation of Marx by Albrecht Wellmer is very close to the interpretation I am trying to develop of Habermas (after taking the difference between Marx’s and Habermas’ position into account). Albrecht Wellmer is one of the “most interesting students of Adorno” (the words are more of less of Andrew Bowie) working today.
Marx calls his philosophy of labour “naturalism” or “humanism” and he opposes it to both idealism and the older forms of materialism (i.e.; in particular the “physicalist” materialism of the eighteenth century). “We see here,” Marx states, “how consistent naturalism or humanism is distinguished from both idealism and materialism, and at the same time constitutes their unifying truth. We also see that only naturalism is able to comprehend the process of world history (Karl Marx's early writings, ed. T. B. Bottomore p. 206)."Habermas on Peirce". ” In the first of this theses on Feuerbach Marx summarizes concisely what he means by his dialectical overcoming of both idealism and materialism: “The chief defect of all hitherto existing materialism – that of Feuerbach included – is that the thing, reality, sensuousness, is conceived only in the form of the object or of contemplation, but not as human sensuous activity, practice, not subjectively. Hence it happened that the active side, in the contradistinction to materialism, was developed by idealism – but only abstractly, since of course, idealism does not know real, sensuous activity as such.(Marx's and Engls' Basic Writings on Politics and Philosophy, ed. L. S. Feuer, p. 283On critical theory / edited by John O'Neill, p. 231]
Habermas like above criticises what he calls strong naturalism of Quine and others (including what he disparagingly calls “empiricist" tradition as a whole) for neglecting the active side of the subject (subject of course re-conceptualised in accordance with the requirements of linguistic turn and emphasis on intersubjectivity) and for that he still turns to “idealism” and try to incorporate that into his overall naturalistic framework. Similarly he criticises “strong” idealism for neglecting the material, naturalistic side. Habermas’ aim, like Marx, is to synthesise the active side of “idealism” and the “passive” side of materialism in an overall naturalistic framework. This is the aim of Habermas’ weak naturalism.