Is the front system residual valve in backwards? It shouldn't keep you from getting any pressure (as you describe) but it would make the pedal 'spongey' (like there was air in the system).
What kind of proportioning valve do you have? If it's a combination valve, could it be in backwards?
X2 on bleed the MC at the fitting.
You say no leaks and power brakes, could the front circut be leaking into the booster?
