Creative labs sound cards a for people who want to play computer games. There D/AC's have improved but are still week. The are not pre cards they are consumer cards. Don't take my word for it have a search through HR.com or even this forum to see what people have to say about them.

Near field speakers work by being very close to your ears. THis negates much of the rooms acoustics.

Flat response means that the speakers don't color the sound to artificially make it sound nice like stereo speakers. this is bad as when you get your mix right through the pare you are using it wont necessarily translate to another different pare of stereo speakers or a car audio system for example. Headphones are the same. They make everything sound nicer than it is and this can result in some very unpleasant surprises later on ! If you are very experienced it is posable to get away with mixing through headphones or stereo speakers however you have to know your kit very well and know what frequencies are distorted. It is even then sometimes very difficult to hear if something especially a vocal line or harmony is in tune. Always best to check it on a few different speaker system (like a car stereo, a boom box etc) before playing it to anyone.