I agree with your own caution on being too martially critical as this will make the professor *personally* defensive and thus reluctant to change.

While - in theory - suggesting that the professor observe (presumably exemplary) Professors Mandy and Jim in the same department *might* work for *some* staff, it is more likely to backfire as the external behavior view is so different to the internal motivation feeling. And there is also the matter of professional pride: nobody wants to be anyone else's clone.

From your information, I think the main problem is the monotone and how it affects the allocation of attention-focus by students - who are likely writing notes concurrently: the professor is not changing his tone to match the importance of the immediate point.

I think the solution to this might involve something like what is used in "labs" for foreign language learning, e.g. something that plays a dialogue on some ordinary scenario between native speakers that the learner may listen to, repeat, hear his own recording and repeat till he adjudges his pronunciations adequate. Of course, here the topic is not an encounter between a travelling salesman and a train conductor: it's about an advanced field of study. And likely no examples exist for that field. However some public lectures, e.g. Royal Society Lectures or Open University course lectures (see [YouTube][1] or [the OU website][2], exist where the speakers have been given a reasonable amount of on-camera training. 

But before the latter could be of benefit, the categorization and hence objectivization (i.e. de-personalization) of this problem needs to be done and it is best that some members of your class approach your university's Teaching Support Unit (or whatever it's called over there) and bring the professionals there onboard with you. If their terminology for this issue is for example "tone modulation", then refer to this term in your critique to the professor.

But the good thing in all this is that the professor's own goodwill to want to teach  you his subject and guide you in your researches. So many bad teaching staff simply do not have this - and this apathy is palpable and itself sows apathy in the souls of students.

I think this guy will come through if supported by colleagues and the university's teaching support bureau.



  [1]: https://www.youtube.com
  [2]: https://www.open.ac.uk/