I have an AudioSource Amp200 and I second Gonk's recommendation to make sure the switch on the back panel is set to Trigger. Also make sure you're using the Line 2 input as that is the primary input. When a signal is detected on Line 1, it switches to that but once the signal disappears it reverts to Line 2 (the Delay Time setting controls the length of time between loss of signal on Line 1 and the switch over to Line 2).

If the bright, obnoxious light on the front stays blue between songs then that suggests the Line 1 / Line 2 scenario. If the light changes to retina-searing red then the amp is actually turning off so the problem is the power-on setting...