Good question. I am no master. But I think the spidif output is probably out 1 + 2. On most of my gear out 1 + 2 is duplicated on the spidif out.
The analog outputs do sound much better than the USB outs into your host. If you go out the Virus outs 3 +4 and back into it's input, you can get great recordings of your virus. Just make sure you aren't creating a feedback loop. Try it for yourself !
: )
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SH- 101, BassStation, Alesis Andromeda, Novation Nova, Virus TI 3.0.3 , ATC-1, Waldorf Blofeld... Lexicon, Line 6, Boss.... 96 Point Patchbay 
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