well that's my point - you said that 'those who held Marx to be the last word in philosophical modernity, and who regarded Hegel and the whole idealist tradition as outdated and superceded, actually missed what was most important in Marx and were left with a philosophy which returned to an earlier, Kantian epistemological problematic.'
then when asked what was the most important in Marx - you reel off a bog standard Kantian epistemological speel - so on one hand you're criticising those who returned to an earlier kantian epistemology as they missed out on the what was most important in Marx, yet when asked what this most important thing was you give a standard kantian epistemology
maybe i've not picked up on the context in which this is being discussed as its looks boring as shite - but what you seem to be saying is that whether people missed out on what was important in marx or not, they end up at the same place, your kantian epistemological - as whether they degenerate back to kant or whether they get what was most important in marx - both these things, in your words, are the same