Have heard both in the same system but not at the same time. They are very different. I own the Gen VIII S3. Actually a tube preamp with the Gen VIII gives the best sound. The Gen VIII provides very tight bass that a tube preamp might not otherwise have.
If you were deciding between one or the other, I would not know which to recommend. Either choice would be a trade-off in comparison to the other in some areas. If you listen mostly to vocals and chamber music, I'd vote strongly for the ARC Ref II MKII. However, if you like very dynamic music, the Gen VIII excels in this regard.
If you were deciding between one or the other, I would not know which to recommend. Either choice would be a trade-off in comparison to the other in some areas. If you listen mostly to vocals and chamber music, I'd vote strongly for the ARC Ref II MKII. However, if you like very dynamic music, the Gen VIII excels in this regard.