I have to agree with my brother. I tried keeping my older transcriptus with a pair of kribensis that were larger than him, and he kicked them all around the tank and back. Not to mention that I have read a few places that kribs can kick rams around. So, if the transcriptus can kick around the kribs and the kribs can kick around the rams... then the transcriptus would probably kill the rams, right?
While 7.5 might be okay for the rams, Tangs (like the calvus's mentioned) need higher pH, I do believe the 8 should be the minimum in most cases; however, I can say they can adapt to lower pHs from personal experience.
Here's what rams like for water:
pH between 6 & 7.9 (depends on what the breeder used)
gH, between 2-(probably) 10
Temperature, they do better with the temperature above 80
Here's what tananyikans like:
pH between 8 & 9
gH between 12 & 20
Temperature, best at somewhere between 75-80F
Mainy, rift lake cichlids and any new world dwarf cichlid are simply not compatible due to the different requirements for water.