With no trigger on your amp, there are still a few options. The
Craftsman 24031 Auto Switch will create a switched outlet that is triggered by the current draw on another outlet (such as the one powering the 990). For a bit more investment, you can look at power conditioners and surge protectors that will provide some protection as well as some trigger-controlled switching. One example is the Belkin PureAV line - the PF31 and PF40 offer switching the high current outlets as well as some other outlets from a trigger like the 990's, and the PF60 allows you to specify which outlets are switched (on my PF60, only the high current outlets are switched by my 990). You can do similar things with Panamax power conditioners, but eCost often has some really good deals on Belkin PureAV that includes Belkin's warranty (eCost is an authorized dealer). Some examples:
PF40 ,
PF40L ,
PF31L , and
PF60 .