Full Volume Through External Speakers

You've heard right, in a sense. Even the most expensive speakers can be "blown" by trying to push too much voltage (i.e. volume) through them.

You say that the external speakers have no volume control. Does it use batteries or external power at all? If not, then I wouldn't worry too much. The iPod touch's headphone jack doesn't deliver enough power to damage the vast majority of small external speakers by itself. I'd worry more about getting tinny sound that lacks in the bass department.

However, if it does have batteries or an AC adapter that amplify the incoming sound, then there is a risk of speaker damage. If this is what you have, set the iPod touch's volume to low or medium power initially, then adjust slowly upward until you reach a volume that's loud without distortion.