How to make my speakers louder?
This is to do with amplification. The sound output from the normal headphone jack is not amplified. Your speakers are not amplified either. On your previous setup there was an output socket which was pre-amplified. Just buy a set of amplified speakers and carry on using the headphone jack. There is no way to make the headphone jack amplified. If there was, some people would use it and blow their ears off with their headphones.