That's not a KDE issue. But the short answer is "No." If all of your volumes are set at 100%, then they're already at their max.
The exception to this rule, is that the sound stream itself can be modified--generally by compressing the dynamic range of the audio, so that quiet sounds seem louder. Technically, this degrades the sound quality, but may be what PulseAudio (whatever that is--I've never heard of it) does.
Your best bet is probably to buy better/more amplified speakers.
EDIT: I don't know of anything that does dynamic range compression, as mentioned above, on they fly in Linux, but ALSA is very configurable, so I'm sure it could be done with enough research and effort. But at my hourly pay rate, I could buy a lot of really nice speakers for the time it would take me to figure out how to do it in ALSA... and the results would be better with new speakers.