Originally Posted by terrier

That site has never covered Spain, unfortunately, and I'm not aware of one that does. But equipment choice in Spain is frequently dictated by the infrastructure - e.g. whether the train has to support diesel operation for part of its route, or switch track gauges. (Only the high-speed network in Spain is on standard gauge; the older network is a broad gauge unique to Spain and Portugal. The trains capable of gauge changes are all pretty similar inside, because they're all locally-produced Talgo equipment.)

If the train you're interested in allows for advance seat selection (e.g. on an Elige fare) you may be able to identify the specific equipment scheduled by making a dummy booking on renfe.com.