Control volume level of RCA audio output on 32PFL3504D

Hello, I have a 32PFL3504D TV that I would like to use a pair of powered speakers with. The connection is trivial, but I find that the TV does not change the level of the line-out with the normal volume control. Since the speakers are just speakers and not a receiver the only way to adjust their volume would be to physically turn their volume knob down, so I'd like to control this via the TV remote. Even with the tv speakers turned off the volume level of the RCA-outputs is constant, and therefore useless. Any suggestions?

have ask for that feature five years ago

in last year's firmwares i can see only downgrades such as:
a) lose of option `Delta` - set volume correction for particular chennels and inputs
b) option move picture hided somewhere deep in menus, before were on Up/Down/Left/Right buttons
c) button OK does nothing, before were channels+sources list there