1. This distortion happens when the Audia's output is sent to the Pass. It occurs whether the connection is RCA or firewire/XLR.
2. The distortion does not occur when the Audia's output is sent to a headphone amp.
3. Therefore, this distortion is originating in the Pass (or the speakers, though that's unlikely IMO).
As I posted originally, lack of headroom is unlikely to be the problem. Atmasphere (who builds amplifiers and understands these matters better than I) has frequently posted that preamp circuits with slow slewing rates can exhibit distortions that sound much like mistracking. Slewing distortions are most audible on dynamic peaks with hard blown horns, strong vocals, etc., and they have little to do with a preamp's overall headroom or lack thereof. SS circuits, especially less expensive ones, are more prone to this.
Based on the information provided, this would be my guess. You could confirm by substituting another component for the INT-150 (perhaps higher end separates).
2. The distortion does not occur when the Audia's output is sent to a headphone amp.
3. Therefore, this distortion is originating in the Pass (or the speakers, though that's unlikely IMO).
As I posted originally, lack of headroom is unlikely to be the problem. Atmasphere (who builds amplifiers and understands these matters better than I) has frequently posted that preamp circuits with slow slewing rates can exhibit distortions that sound much like mistracking. Slewing distortions are most audible on dynamic peaks with hard blown horns, strong vocals, etc., and they have little to do with a preamp's overall headroom or lack thereof. SS circuits, especially less expensive ones, are more prone to this.
Based on the information provided, this would be my guess. You could confirm by substituting another component for the INT-150 (perhaps higher end separates).