I’d actually argue that a simple potentiometer based volume control, or a fixed resistor divider (both having the same effect), would be more appropriate than a transformer - unless you specifically need galvanic isolation or want to hear transformer coloration in which case you already know what you want.
Why? It’s both vastly cheaper, and does the job as well as you’d want to with an unbalanced, line level (or hotter than standard line level) signal and modern gear. Fixed resistor pads are ubiquitous, and you’re likely to have and use attenuators / mixers in your modular anyway. Low distortion, no discernible change in sound quality, just a quieter signal.
(Edit: I see transformers used for balancing and impedance matching a lot, but it’s pretty rare to see them used in circuits for attenuating a line-level signal. There’s nothing inherently wrong with that either, but a resistor divider will just be neutral, effective and super cheap, so there’s not much reason to use anything else unless you know you need something else than simple attenuation.)
