I have an Emotiva XPA-2. It sounds great to me and I'm driving B&W 802's with it. Pretty much everything I read before buying Emotiva was positive. Most negative comments are from people who have never even owned the product and think because it is a bargain for the money, it must not be good.
As far as the UMC-1, a lot of people are gun shy on this product. It has been in pre-production testing for a long time and has been delayed several times. It is likely that Emotiva is trying to work out all the bugs. As of now, it is supposed to be out in March, but it may still be buggy. A lot of people here are holding off or buying other Pre/Pro's/Receivers to do their processing. Emotiva has great customer support though, so it may be worth getting if you don't mind having to do firmware upgrades as time goes on.
As far as an Amp though, they are solid and you can't really go wrong. They offer a 30 day trial on their product, so the worst case scenerio is you could always send it back if you were unhappy. I doubt you will be though....