The thing about USB in general, particularly the older implementations (such as the version 1.1 mode of the Virus), is that regardless of throughput potential, they tend to not perform well with regard to latency-sensitive tasks. USB just wasn't designed latency in mind as a high priority. It can perform well enough for some things under some conditions, it's just far less reliable than the alternatives.
For example look at the Focusrite audio interface lineup. For their Firewire or Thunderbolt interfaces, they advertise near-zero latency, but they don't make that claim for their USB products. There has to be something to that.
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