Should I use the volume control on the rear of the A2+s or can I adjust from system volume on my computer?

If the left speaker is in an easy to reach location, you can certainly use the physical knob to set volume. If not though, it's perfectly fine to set the A2+ to a good volume and adjusting from source. Every setup is different, so some experimentation will be necessary to find your prefered settings, but around 11 or 12 o'clock is a good starting place.