A speaker's wattage is the maximum power it will take before the coil burns out. If you're not putting 2.8W into it you won't hit its "maximum volume", but in practice "maximum volume" is likely much too loud for most purposes.
We've found that the larger (physically) the speaker is, the better it sounds, no matter what the wattage is. We use this amp with 6" 20W speakers with surprisingly loud and great sounding output.