I may be speaking outside my portfolio here and if so will be rightly challenged and corrected. I have a range of alembics, filter and non filter based instruments including a series II and the sound quality is the same on all of them. The differences are because they have differences in pickups and electronics, build materials, scale length, hardware such as tone blocks or not, and pickup locations etc, they have differences in how they sound and importantly how their sound can be shaped to your needs. But they all have that high end sound quality.