Audiocontrol 2 channel input?

I assume what you mean is could you use an Epicenter with your HU?  You could assuming you also have a good crossover, but you don't need it.

The Epicenter requires a full-range input, so you'd need to drive it from either your front or rear output (not your subwoofer output.)  Then you could use the 24XS after it to crossover the signal with low-pass to your sub amp and the high-pass output to drive either your front or rear amp.  In this case you would not use the sub output from your HU.

The only real reason to use an Epicenter is if you are trying to get more out of cheap or undersized subs than they are designed to produce.  The Epicenter is a digital synthesizer that creates bass information not originally recorded on your CD.  If you have a decent sub system, an Epicenter will most likely only cause problems.

Do you own either of these AC units or are you simply thinking about it?  If you're thinking about it, don't.  Spend the money instead on the best speakers and amps you can afford.

First of all, the MBQ PWE-160 is a 6.5" midbass driver.  What are you trying to accomplish with these?  What are you using for mains?  You do not need a crossover for the sub as you can use the HU built-in LP filter, or the one in the amp. 

OK, so it's the component set which comes with its own dedicated passive crossover.  Good speakers.  Unless you plan to biamp the components, you should use the supplied crossovers. 

You have a 4-channel amp that should be run from the friont and rear outputs from the HU and a sub amp that should be run from the subwoofer output on your HU.

Why do you think you need to use an extrernal crossover?  I can see NO reason why you need one.