Well ideally you'd like to have both types of shielding to break up EMI fields. The internal shielding is undoubtedly more important than a tin cap.

I am sure that Asus would have also taken this into consideration as they are experts in this field....
Another reason I got the Asus card as well that I can use it as a digital transport to an external DAC without having to use USB when I would like to upgrade to a better DAC. It is the same reason why I like the Musiland Monitor 01 US as I can always decide to use it as USB->SPDIF converter later. I am betting though that this unit will change my perception of USB as a great interface for audio..
Pity we can't organise a get together so everyone could try out the different audio interfaces. Would be very interesting to see all the differences!