USB outboard sound card comment

I've reviewed the technical specs for over 20 of these boxes all different brands. Not one of them indicates whether their USB interface is 1.0 or 2.0. Big difference. What's with the "sound card" world?
I would bet they are all version 2.
Please keep us informed as to which card you go with and why.
I have the Waveterminal U24 and am very happy with it. It is a USB 2.0 device but is backwards compatible with USB 1.0. I'm pretty sure most USB2.0 devices are backwards compatible. My Macs are all USB 1 and I've never had any problems streaming audio with them. USB 2.0 has a significantly better data-transfer rate, but in my experience with Mac/Waveterminal/iTunes it makes no difference. If it is not streaming music fast enough you would get pauses in the music.

I have a TwinDac Plus. It is really an outboard dac, not a soundcard. it has a usb input though. It requires USB 2.
I just purchased a Firewire version of M-Audio Audiophile. Time will tell. I understand USB 2 has even a better bandwidth then Firewire but I was unable to distinguish which devices are USB 1 or 2.
I also am of the understanding that normal 16/44 CD data rates can be handled just fine with USB1. It's when you get into the 24/96 that having USB2 becomes helpful.
Peter_s is correct - USB 1.0 is more than adequate to handle 16 bit 44.1 KHz data streams. USB 1.1 handles 12 MBits/sec and cd-quality audio requires 705,600 bits per second (16 * 44,100). 24 bit 96 KHz requires 2,304,000 bits per second so it, too can easily be handled by a (dedicated) USB 1.1 interface.

Where things get complex is when you're sharing devices on a single USB bus, such as an external hard drive (note that most computers have a single USB bus with multiple ports - i.e. two USB ports does not mean you have two USB buses). USB 2.0's additional bandwidth will help here and prevent data choking/collision.

The other area that a lot of these external audio interfaces is used in is for home studio recording, where you (may) need multiple channels of audio running simultaneously. USB 1.1's limited bandwidth chokes on 4 simultaneous channels, which is unacceptable in many situations.

With all that said, why even bother paying more now for an interface that can support USB 2.0 or 24/96? When the 24/96 formats come out for software they will surely have some form of hardware DRM (digital rights management) that the current generation of audio interfaces don't have.
I, too, did research when I bought a USB-based sound device - M-Audio Audiophile in my case - and discovered that the worse problem was contention on the USB bus rather than an issue with 1.0/2.0.

I ended up getting another USB controller card for the old Dell I use and isolated the M-Audio on it. This has worked well now for over 2 years.