The 480 has 1 additional pair of transistors per side, in addition to a beefier power supply. This would imply better control over bass and impedance dips, especially around 100 Hz (based on the single impedance curve I found for your speakers).
On the other hand, if you like the sound, having a stiffer amp may change the tonality. If you listen at low volume most of the time, stay where you are. If you want to turn it up and could use a little more punch, upgrade.