Not having a wiring diagram, its difficult to diagnosis reasons for tach and EML, but depending on wiring, it might not mean anything. If there are diodes in the wiring harness you could get feedback on one side and not the other, resulting in the EML situation. The tach might read off of one side only; in fact, it probably does (how could it read both sides at once?)

One thing you might not have checked is the solid state mechanism which actually breaks the circuit on the primary side of the coil (i.e., whatever electronic widget is doing the job that the points and condenser used to do in days of yore). Your symptoms sound like a condensor failure, but since there isn't one, it could be whatever performs that function. I doubt the DME actually carries the current for the primary wire, as that would be an awful lot of current for a digital device; it likely just triggers, remotely, a high-current solid state device. If you can find such an anminal, and there should be one for each side of the motor, you might try swapping them to see what happens.

My 88 750 misfires most notibly at highway speeds (sometimes of idle). Also, the idle is not as smooth as it should be. This condition appeared abrubtly one day.

I have narrowed the problem to the left cylinder bank (7-12). If I pull the fuel pump relay and DME relay for 7-12 bank then the engine attempts to fire and run but will not. I receive no EML light during cranking and the tach responds. The engine will run on cylinder bank 1-6 but I get an EML light and the tach does not respond.

What I have tried so far:
1. Switched coils side to side.
2. Switched DME's side to side.
3. Switched mass air flow sensors side to side.
4. Measured electrical resistance of crankshaft position sensors. Each sensors measure identical and within specs.
5. Measured intake air sensor resistance...within specs.
6. Verified fuel pump working (audibly) for left bank (7-12).

What I have not done:
1. Checked rotor and cap resistance.
2. Checked plug wire resistance.
3. Checked coolant temp sensors
4. Checked oxygen sensors.
5. Fuel pressure and fuel pressure regulators.

Anyone have any ideas as to why cylinders 7-12 wont run? Why I get no EML (7-12) or why no tach on cylinders 1-6? Obviously cylinders 7-12 are partially working otherwise I would notice the resultant poor performance and probably get an EML.