I have a good experience with keeping Duboise Maswa and Petrochromis Trewavasae moliro together,none what so ever with those problems written above!both groups where breeding

ps.both type of fish had the same size...
Also a group of Ilangi`s together with petrochromis orthognathus tricolor chaitika,and in this tank there where only 12 ilangi`s and they was the minority...a little video:http://www.youtube.com/watch?v=_xYH1t1JnGs later on i actually added some Julidochromis regani kipilli in this tank still with succes....have heard several stories about petros and trophs together,and in the end it seems like the best solution if u want to try,u will have the best outcome with trewas and tricolors togetger with trophs!
Best Regards
Carsten