One question you might want to ask yourself first is, do you want sound field modes, or are you perfectly happy with straightforward surround and stereo? That can be important because if you want sound fields, you typically need to go with a receiver as a base.
I have yet to hear a Class D receiver based amp that drives 4 Ohm loads as smoothly as a good AB external, but that doesn't mean they don't exist. The issue is, pre-pros are a bit more of a commitment. They may not have the same resale ease and you can't just "demote" them to another system without a spare amp. It's always worth considering a hybrid system, like John Garcia mentioned. The SC-72 would give you that full flexibility. Plus, the UPA-700 is hardly a beast. I suspect it will handle your speakers more easily, but will it have the power you want? On the other hand, if it doesn't, neither will the receiver. The XPA-3, with the receiver powering the surrounds is a good option.
The Hybrid System
The Music Part: Emotiva XSP-1, Thiel CS 3.6, Emotiva XPA-2, Marantz SA8004, Emotiva ERC-3, SVS PB-12 Plus 2
The Surround Part: Sherbourn PT-7030, Thiel SCS3, Emotiva XPA-5, Polk & Emotiva Surrounds.