I find that it is almost impossible to predict how two pieces of gear will interact and sound together. You must ultimately make a choice based on actual trial -- anything else is a crapshoot. Recently, I heard a trial of a 5 watt pushpull 45 amp and a very good tube linestage driving a pair of Sonus Faber Anniversarios in a small room. The system sounded bad -- flabby bass, lacking in dynamics. I thought that it was obviously the way too low-powered amp. It turned out to be the linestage working with the particular amp, i.e., just the opposite of my expectations.
I would not change out the Pass Labs linestage for anything else unless I actually heard the combination. Generally, maintaining the same brand of equipment work well together; mixing may work, but that must be carefully evaluated.
That said, I do have some very general impressions about candidate linestages. Other than with the Ref. 3, I have not heard any system that had an AR linestage of recent vintage that I liked. In several systems where the Ref. No.2 was being tried out in, the system sounded a bit too lean and harmonically bleached for my personal taste. The BAT is perhaps a touch lean too, but not anything like the AR gear and it has a terrific remote control and a lot of flexibility. I would also suggest that you look into the VTL 7.5. I heard several nice systems that were controlled by this linestage. It to has a very good remote control.
