Herman, the experiment you describe was the first one I did when I got the DAC1 a while ago (I started out with a Airport Express and a Macbook with optical out)...
The differences between 1) and 2) were similar to the more recent experiment but even more pronounced. Similarly for the Airport Express which I also have. In fact, I was expecting the transport to do much better since it is isolated from the PC, but I guess that is not necessarily the case.
Certainly the observations are true for the Benchmark, which is the DAC Henry was considering. In fact, your experiments with the Altman are more of a singular experience, since Altman put great care in the toslink interface ;)
A better comparison would be
1. Mac Mini feeding Benchmark DAC1 via USB
2. Mac Mini feeding Benchmark DAC1 via toslink
even though this isn't conclusive either since despite what Benchmark says the DAC may indeed work better with USB. This isn't saying USB beats toslink every time, only that the Benchmark may be better with USB.
The differences between 1) and 2) were similar to the more recent experiment but even more pronounced. Similarly for the Airport Express which I also have. In fact, I was expecting the transport to do much better since it is isolated from the PC, but I guess that is not necessarily the case.
Certainly the observations are true for the Benchmark, which is the DAC Henry was considering. In fact, your experiments with the Altman are more of a singular experience, since Altman put great care in the toslink interface ;)