Seeking soundcard specs & advice

Hi , great info in this forum, can you tell me if there is a comparison chart of controller sound card specs? I have a X-Ponent and the sound quality is OK through my JBL Ion 515 speakers, but playing ITunes on my high spec HP laptop (entertainment series) sounds better at higher volumes, probably because the A/D converters and soundcard are better quality I want to stick a NI Audio 2DJ in my system, where do I place it in this setup: Laptop-XPonent-Extrernal Mixer-Speakers. I mix internally in Torq but use the mixer to input microphones and CD players etc. The mixer is not connected to my laptop via USB. Also thinking of ditching the XPonent for the VCI-100 after all the DJTech work on mappings and button upgrades. My friends use Tractor Pro, though they are using time code and turntables and scratch a lot. I dont scratch but like to use the platters for cueing drops and loops with the occasional scratch or spinback. What do you recommend ?