ok
so i see your arent exactly the patient type. your point has many answers. the cards you mentioned are all decent, 24 bit is better then 16, go for bits over extended frequency first. but how many inputs do you want. the ones you were talking about had 4. the 424 has the A/D converters inside the computer this introduces noice into the card since its closer to a lot of processes. The 296 obvious has the 96Khz capability. and if i remember a break out box so the converters. Ten you have the Echo cards which are all break outs so that is a good start, anywhere from 2 to 8 inputs. i mean the list goes on to more expensive(and better) A/D converters. go make spreadsheet. list price, inputs, bits, Frequency, MIDI, Wordclock, SMPTE, balanced, unbalanced, and watever you would like to consider, ability for digital in and outs. etc you probably will have a lot better ideas then.