I recently noticed that a hi-end tube audio manufacturer in Vancouver made a 100 step IR remote control volume passive pre-amp, model number RV-101, which should be exactly match your requirement. They claim this is all relay switch resistor ladder type with best sound. Only one input and one output. They have a website, just type www.space-tech-lab.com to check it out. The guy run this shop is a real nice one, I have been there several times, he make really good sound tube equipments.
