Paul Spasske asked that I post the results, and since this may be a common problem in the future for 700 series owners, here it is:

As I had previously mentioned, I had changed the Halls Effect sensor, distributor cap, plugs & rotor as well as swapping out the Ignition ECU, Mass Airflow Sensor, coil and fuel injection relay. One of the reasons that I had mentioned that the tach needle died immediately is that fuel problems allow the tach needle to wind down. I'm not a Volvo guru by trade, but I've owned a ton of British cars and this is a common and easy way to determine the difference between an electrical fault and a fuel fault. (Wet plugs are a good indication of fuel too, I guess!) When I was in the Marines, we always used the KISS method (Keep It Simple Stupid). It still works well, and I always try to remember that MOST (not all, those British cars are different!) vehicles are pretty common when it comes to the wiring and basic function of their systems.

I posted my post again because I had basically changed or swapped everything I was aware of in the ignition system. Paul Spasske's suggestion to try the Power Stage was simple and quick, and yes, it solved the problem. (I forgot about it being an integral part of the ignition sequence.) There's a Volvo dealership about 3 miles down the road from me, but they're a lot more interested in selling the parts than helping solve a problem. That's one of the great things about internet forums. Chances are good that someone has had the problem in the past, and at $71 a hour labor rate, I'll take my chances at posting first.

Thanks to all that posted. My many humble thanks to Paul for pointing me in the right direction, but all of your suggestions were valuable!

Cheers~
Keith Miller
Hendersonville, NC
www.angelfire.com/nc/jandtautomart