One is already in production from Audio Synthesis, a British high-end company. I'm using one right now in tamdem with a heavily modified EAR 834P to play vinyl. The product is called Pro-Passion. It has one balanced input and one balanced output; simplicity in the extreme! Let me just tell you that once you've had a taste of what a passive preamp can do - when properly used within its limited parameters - you will shun and despise all active linestages!
