My guess is that the midrange will be a little peaky, since the 8 ohm tweeter will "try to go lower" on the 4 ohm crossover, than it would on its proper crossover.
It will probably be fine, as long as you keep the volume down. Crank it up, and the extra "energy" in the mids to the tweeter, due to the impedance mismatch, might damage the tweeter...
You could always parallel an 8 to 10 ohm, 5 to 10 watt resistor with the Large Advent tweeter, and see how that works... that would make it "act" like about 4 ohms...
Regards,
Gordon.