Are you fixed to use an Amiga sampler or could you life with some other/better device that record your samples at 16 bit and afterwards convert it to 8 bit? You have less noise but still enough.
The problem with 8 bit resolution is that you are more or less forced to sample at max volume. The lower the volume of the source is the worse is the recorded quality. What you notice with the "quiet orchestral passage". So, a preamp kind of device between source and your sampler would be nice. I use a mixer that do the trick.