The DMP3 and the Tampa do sound different from each other. But, what you use your money on completely depends on what you need? Do you really need an outboard compressor like the RNC or the one that comes on the Tampa?
Also, I don't know what other people have to say about this, but I don't think that you should go out of your way to avoid using only one pre on a recording. If I the only two pres I had were something like a DMP3 and then something like a Great River, you better believe that I would most likely only use the Great River. But, when you are in the range of things like the DMP3 vs. the Tampa, you're talking about different colors. So, in my experience, it's best to learn your gear as well as you can and use it to its maximum capability. Such as, I have noticed that the DMP3 tends to give cleaner sounds when on the low-gain setting than on the high gain setting (but, I recommend that you experiment on your own). So, you could use that knowledge to help get better sounds in the recording.
So, if you're looking into getting a second pre, you may want to look at the Tampa. But, there are definitely other options in the price range, such as The Brick. But, it all depends on your needs. Do you need the compressor on the Tampa? Do you need the digital output? How many channels do you need? Tons of questions.....and yes, I guess all of that is common sense.
But, back to your question...I don't necessarily think that you should avoid using one pre for the entire arrangement because you can get different tones and colors out of one pre by learning the ins and outs of it. Whether or not the Tampa sounds different than the DMP3 will be based on your ears. I think that they sound different. Other people don't. I'm not really sure how the RNC fits in here. But, if you need a compressor, get a compressor. I've never used the RNC. But, I've heard good things.
