Apogee Mini DAC: Connection questions

I have recently purchased an Apogee Mini DAC. It sounds incredible. I bought the non-USB version and am connecting it to my computer via a U24 Waveterminal card. I have a couple of questions:

1. Would I get a better sound if I purchased the USB card unit for the Mini-DAC? Or is the sound better going from a quality external card like the U24.

2. I am currently using a glass toslink to connect the mini dac to my waveterminal. I have heard people say coax is better, but others have said toslink is better when computers are involved. Any insights?

Thanks.

dshea