I was in the same quandry as you, and I spent hours on the search function here researching cheap pre-amps. I wrote down all the ones you mentioned plus others and did google and ebay searches etc.
From what I gathered in these many hours was that unless you want to spend over a grand, there was real step down when you get to the under $1000 options. But, I don't have a grand.
From what i gathered from folks opinions, and there were a lot, it was either the DMP3 or the RNP. The RNP rarely sells for less than $400 on ebay, so its a lot more $. I have not used it, but based on everyones description it is the bomb for it's price, much like the RNC.
I did get a DMP3 on ebay for $100. I have to admit, I really did notice a quality differance over the preamps in my Alesis board/mixer. I think if you can get it for the $100 I paid on ebay you will be pretty happy.
That is, according to the very knowledgeable folks here), untill you can afford the $1000 ones, and someday I hope to save the clams to buy one too.