Who makes the best passive volume control?

Silver Rock.....

Any of the Reference Line models. Reference Line was the "reference" pre-amp for a number of equipment reviewers because of its neutrality and transparency. Plus the dynamics is incredible.

I've had the Adcom 750 and the Placette remote volume control. Placette is a little better, but the Adcom provides more features and inputs/outputs and for the money is the best deal in audio.

Channel Islands Audio and NHT both make very serviceable passives, at a very reasonable price.

I've been using the Placette Remote Volumne Control
in balanced configuration,I have not look back since.I have had at home some of the so called audio industry reference Pre-Amp's such as CJ,audio research,BAT,CAT.This unit is so much more musical and grain free.By Far the best investment towards great music.