First of all, speakers doesn't work with digital signals, it has to be a contionous analog signal for the
speaker diaphragm to move and produce sound. Therefore, any digital sound in the end has to be converted to analog before it reaches the speaker.
Optical signals are digital, so the TV cant send analog sound via optical. In that case you either have to use a speaker system with a built in DAC with an optical input, a receiver before the speaker system, or you could use the external DAC that i linked in previous post, connection an optical cable between your TV and the DAC, and on the other side of the DAC connection the two rca- cables between the DAC and the speakers.
But am I going to have to use both the RCA and the optical outputs on my TV? The RCA for the actual TV and the optical for any digital signals (ATV and other HDMI)? Or can they be combined? Evidently, the TV cant convert the digital to analog but should the TV be able to convert the analog to digital so I can just use the optical output for everything?