Dimdim has designed and built his own stepped ladder attenuator, controlled by an Arduino:
A few years ago I had an encounter with a ladder volume attenuator. I loved hearing the relays clicking away as they dialed-in the desired attenuation.
Ever since then I wanted to design and build one for myself. The years passed, with other more urgent projects taking priority, but I always had this thing stuck in the back of my mind. I was doing my research at a very slow rate. Slow, but steady. I came across a number of ready-made ladder attenuators, such as the RelaiXed2, the one from AMB, Vicol, and others. I also came across some uC source code, but nothing ready-made for an Arduino.
Project info at Dimdim’s blog.