I have not used or tested any express card form factor sound cards. None of the laptops I have used in the last 10-ish years have included that slot.
I am NOT a fan of 1/8" connectors. There is limited contact area, and in order to save a few pennies, most manufactures use really cheap connectors. This is a mechanical connection...and it will be exercised every time the connection is plugged in or out.
My preference for the mechanical connectors in descending order are:
XLR (if high quality like Neutrik or Soundcraft or similar)
RCA or 1/4" (beefier connections, more contact area)
1/8" (only if I must...I have converters to turn this into 1/4" stereo or RCA)
JesseMiner wrote:For the past few years I have been using the Echo Indigo PCMCIA DJ card (awesome sound by the way!)
I try to avoid superlatives like "awesome" when describing sound.
To test a card, I start by listening to music. I pick pieces of music that I know well...and that include quiet and loud sections. I like using classical recordings for this purpose, because that are a LOT of different instruments that I can focus on to do comparisons between sound cards.
Next, I do a more "objective" set of tests by playing a series of "pure tones" and structured noise (e.g. white noise, pink noise, etc) through the card, and then record that back onto a computer. I then compare the resulting waveforms for differences.
Obviously the whole signal chain is involved, from the drivers to the card to the recording bus, etc. So, it is difficult to get an "objective" view of a single card...but it is very easy to get card to card comparisons. I start with the onboard card, and onboard line in. Then replace one part at a time until I get the test I am looking for.
JesseMiner wrote:I am open to a USB solution if it really is superior, especially because I have been using, and will continue to use, Traktor which should work great with the card or, obviously, the NI Audio 2.
Traktor 2 (Duo or Pro, and the Scratch variants) automatically recognize all the NI sound cards. The drivers are installed with the software. When used together they are as good as "plug and play" can get.