Hey Zhgutas

sorry you haven't had any interaction here - probably the Xmas phenomenon with people not logging in.

First off I should say I am not really a sports physio. However from your description and analysis I would just make the following points which may or may not be useful:

* Yes you seem to have gathered some evidence now for it being an impingement problem
* The chronic nature of the pain - 11 years - i don't think you can rely on pain being closely related to organic impairments. The pain perception may have become a main feature the problem itself
* I would also query whether inflammation is a key process - wouldn't what we know about tendonosis more likely apply. The fact that he has pain at night gives some weight towards inflammation but that might just as well be to do with lying on the shoulder. As an index and test for inflammation one thing you could check if there is morning stiffness and pain on elevation and how long it lasts. +ve response to NSAIDs doesn't necessarily mean an inflammatory problem. RICE hasn't been shown to be effective for combatting inflammation except in the very acute so it is unlikely to reduce inflammation at this point and if you get a positive response to using ice it could just be neurally mediated analgesia or placebo. However working this out might be quite important in working out how to set and monitor exercise dosage.
*what about analysis of postern and presence of muscle imbalances? What are his thoracic spine, shoulder girdle and neck like?
Yes getting some imaging might be worthwhile - is an Wikipedia reference-linkMRI and or a sonogram available?