USB 1.0 Unsuitable for Multitrack Recording
There are plenty of USB 1.0 audio interfaces out on the market, and some of them tout multitrack recording functionality. Be wary however of any USB 1.0 sound interfaces as a digital multitrack recorder as the interface does not have the juice to cater for anything more than 2-in/2-out.
Your numbers certainly get tight if you’re wanting to experiment with 24-bit/96khz audio. Most interfaces will not do 2-in/2-out at this quality level in full duplex. Full duplex refers to the cards ability to record audio and playback audio at the same time. In general, you would want this for multitrack audio, even if it was just for monitoring the performance while recording.
A better option would be to go for either PCI, PCMCIA/Cardbus, FireWire or USB 2.0. All of these above interfaces are best suited to multitrack audio conditions.