4yanx, I understand your concern about inserting an Amazon IC in the chain. I offer a couple of thoughts. First, the Amazon is a very good IC. Second, there is barely 6" of it. And third, there is probably more wire than that on either side of it inside the pre and amp, and you don't know how good that is. Personnaly, I think the many benefits you gain from the high pass filter on the performance of the amp (e.g., reduced power requirements on the bass) more than outweighs any consideration on the effect of inserting that filter. You are gaining, not losing. So, I would advise you to pick your ICs based on how they sound, just as if the filters were not present. Think of the filter and its pigtail as another component "box" you can't really control.
Fsarc, there is a close long time relationship between Richard Vandersteen and Bill Lowe, and it is no coincidence that Richard is using a battery bias in the filter and Bill is using the battery bias on his wires. And, you can surmise why Richard uses AQ wire on the filters.