If they are listed as L-pads, don't use them. If they do not match impedance, be sure not to put too many in parallel.

I once installed about six of these in a system.

What an L-pad does is ensure that the load is 8 ohms from zero volume up to full volume. This is of great value when adjusting the level of a midrange or tweeter in a speaker; if the impedance varied, the crossover frequencies would change as you adjusted the level.

Anyway, room levels were not independent. If you turned one room all the way up, the others went down a bit. More rooms up, all of them sagged in volume. I ended up removing these for free (the job was for my dentist, no desire for acrimony there) and replacing them with Mortronics transformer volume controls.