All small speakers that are operated like headphones can be connected. In addition, also those that have an internal power supply with their own signal amplification. Larger speakers intended for connection to a stereo or home cinema system will not work when connected directly to the converter. Such speakers also hardly have a suitable headphone jack plug, but RCA plugs, large banana plugs or eyelets for screwing onto an amplifier or receiver output, in the past also DIN plugs and the like.

Unfortunately, I can't answer this question because I only use speakers with a preamplifier. The output is strong enough with headphones. Directly on loudspeakers rather not.