Originally Posted by Ragsters
I dont know how to answer that question. I just need something that is good enought to replace my Soundblaster Z.
DAC - digital to analogue converter
. Practically every device has a DAC chip, but in some cases they can't deliver a clean line level signal to an amplifier, so people get a separate DAC. Or one piece of equipment that has a DAC and amplifier in it.
Preamp output - If you want to use studio monitors as well, then a preamp output lets you control the volume on both (they have separate amplifiers on each cabinet). Many use these primarily due to near-field listening, secondarily also because they have separate amplifiers on the the tweeter and midwoofer, which means you can adjust the gain on the tweeter in case the overall sound is too bright/sharp (or if it's too dark/dull).
In your case since you just need to replace your SoundBlaster Z, and assuming you don't need speakers nor can I presume you're going to use a headphone that's relatively hard to drive, just go with the SoundBlaster G5. It has a DSP, DAC, and headphone amp chips in one box, powered by USB. As long as the headphones you use can get loud enough without getting distortion out of it then this will work well enough.