eh ?
what works fine on your macbook ?
You can't plug usb into the iPod touch.
Why would you want to plug a third party sound card into an ipod touch?!
And you would need an adaptor to turn a traditional headset into one of those all in one connectors that the ipod touch / iphone / most other smartphones seem to use.
I would hope that the sound would improve - both for music and Skype. But it may not be as necessary compared to the macbook with its greater electrical interference inside.
Just use the apple iphone earphones & mic ? Afaik it works fine on the iPod touch.
There are adaptors that can turn the two connector headsets into the single connector ones compatible with the iphone. Whether or not this works with the touch I have no idea.
I have the connector the other way myself. As my in-ear headset is an audiophile quality one (not the crappy Apple ones) and I use them at LANs etc.