From my experience with the Vifa 7" mids, they like a lot of power. I had originally powered them with 80w and it wasn't enough IMO. I now have 150w going to each component set and they handle it with ease (just be careful with the gains). You'll want to keep your tweeter at 6ohm like suggested above, so no worries there. I would suggest a crossover more in the 3000Hz range for the drivers you have.
I had Madisound custom make some passive crossovers for me, but that may be too costly for you. If you are pwering each driver with a separate channel from the amp, then you can just use the amp crossovers. Btw, I love my set, once they get the right amount of power, they sing...
