Why don't you ask the folks at ATHQ.com about your needs. They sould know. They are the ones making the profit on the sale. It seems that you are getting in over your head. The amount of money you are wasting on the 1600DSL module and the cat 6 cable opposed to cat 3 would be more than enough to hire a tech to come in and do it right the first time.
I can see it now you will be asking about hooking it up....then how to program the autoattendant....then how to program the phones....then ...etc.

I understand your enthusiam of how neat it is to put in the phone system. You can hang it on the wall and put out all of the phones and have everyting ready to go and Have a tech finish up, and you can have the WHOLE thing up and porgrammed in an hour or 2.