It's either a pot, some on chip thing or relays switching between resistors. There are some other ways though

I'm pretty sure on most of these preamp players that it's a chip thing and handled in the digital domain.

The Capitole MKI remote control can attenuate the volume in the Analog domain or in the Digital domain. If you press CD, the remote will affect the internal digital volume control, but if you press CD/PRE, the remote will be affecting the internal analog volume control. It is much better (sounding) to use the analog volume control. The front panel kob always controls the volume in the Analog domain. The LCD remote control that some owners chose for the MKI has less functionality than the plastic remote control and does not have the capability to chose CD or CD/PRE.

The Capitole MKII remote control can only attenuate the volume in the Analog domain. If you press CD, the remote will not be able to control the volume, but if you press CD/PRE, the remote will be affecting the analog volume control.

...or at least, according to my google search.

Either way it is in the analog domain as long as CD/PRE is selected.

I can't find anything more that a statement saying that it's an IC controlled analog volume control. Be interesting to find out more.

i can open it again, some time.

And hope that its lovely French craftsmanship lets you put it back together...