One important element about pre-amplifiers that I recently learned about in an Audiogon forum discussion was that you need to be careful to look at the input sensitivity of the amplifier that you are driving with the pre-amplifier. So, if your amplifier has an input sensitivity of 0.5V, then you should make sure your pre-amplifier supplies an output voltage of at least 0.5V. If your amplifier's input sensitivity is 3V, then you'll need a pre-amplifier with an output voltage of at least 3V. I think it may even be preferable to have a much higher output signal in the pre-amplifier that the input sensitivity of your amplifier, but I don't know what the ideal is.
That's just one initial screening tool. Then, as far as brands go, I suppose you just need to try some out. . .
That's just one initial screening tool. Then, as far as brands go, I suppose you just need to try some out. . .