I want to experiment with digital room correction.
On the internet I found out that the Behringer ECM8000 gives good value for the money.
Now I'm looking for a good microphone preamp with 48volt phantom power and chinch output for a Terratec EWX 24/96 soundcard.
Any suggestion?

It all depends on your budget, of course. I assume that cheaper is better because of your microphone choice.

Try out the m-audio audio buddy, a dual mic pre for around $70.

Or you can try a small Behringer mixing board. Make sure to use the direct outs and not the stereo out through the board.

Destron

If you are determined to go the separate mic/preamp route take a look at IBF Akustik for both measurement microphones and preamps. Also worth looking at ETF 5 for room response measurement software.

I have a colleague who had rather poor results with the quality and reliability of the ECM8000, but he may just have been unlucky. Or maybe you get what you pay for

For room correction work you will get perfectly good results even with something like the Radio Shack spl meter (the analog version is a better bet than the digital), it is essentially flat over the frequency range relevant to room correction. More expensive mics, preamps etc are a waste of money for such work as their improved accuracy is in the upper frequency range where room correction attempts are a futile exercise.