But to the topic, I heard the speaker distorting a bit.

Remember that distortion (a) is a function of volume as well as frequency, and (b) might be happening somewhere else in the signal chain. Are you sure it's the speaker distorting? Maybe your PC's sound card is overdriving the line-level inputs of the transmitter. Mess with the levels in the sound mixer applet (the speaker icon in the system tray).

Or even more likely: The distortion could be within WinAmp or within the sound card itself. For instance, if the "wave volume" in the mixer applet is set to full, and WinAmp's volume is set to full, if you crank the bass on the WinAmp equalizer it's going to distort right there in the sound card. (Much like doing the same thing on the empeg's equalizer, go figure. ) Again, mess with the mixer levels until you don't hear distortion. If you end up going with an external equalizer, this becomes moot because you'd set the PC's EQ to flat and control your sound with the external EQ.

Does the X10 amplifier or transmitter have any settings to adjust input gain or output volume? I'm assuming not. But if it did, you'd also mess with those in concert with the PC's sound mixer applet to get the right levels without distortion.

Unfortunately, they still aren't loud enough, or the amp that's powering them isn't. We'll settle for now, though.

Assuming that you aren't yet overdriving the inputs of that X10 transmitter, an external analog equalizer might let you boost gain a little bit.