so, here's my opinion on the matter. If we're considering 10K:10K input transformer, a 10K rotary-style attenuator, such as the PCB mount DACT units would be something to consider as an option for this project. Second, would be the equivalent using relays. This is what I did for my preamp. Yes, lots of relays, I think I have around 70 DPDT relays. Also, with a firmware update, you could accommodate a logarithmic ladder version. This would be a poor choice with the input transformer, but a nice option if you're doing balanced only. Finally, with yet another firmware update (or better yet, toggling an option in the uC) a hybrid with 2 switches closed (at most) could be used, which might prove a possibility with the transformer. Note, all of these versions can be built to any value, 10K, 50K, 100K, etc. by choosing the resistor values appropriately.
Obviously, depending on the maximum number of relays allowed for, there would be different step size depending on the version selected. I think think would be okay. In fact, a daughter board could be supported that would add more relays. This approach would be extremely flexible, and in my opinion this would superior option to the TPA JT attenuator. For example, this setup could easily accommodate a transformer volume control (TVA) or autoformer as well as resistive attenuation.
Thoughts?