Don't know if this helps, but just looked in an AMX module I wrote for an Aquavision.
SEND_STRING DVaQUA,"$0D"
WAIT 10 SEND_STRING DVaQUA,"'POWR01',$0D,$0A"
Similar for power off. In case this doesn't make sense, it sends a carriage return, waits one second, then sends 'POWR01' carriage return, line feed.
Other commands do not seem to need the preceeding carriage return.

I cannot remember doing the programming, but guess it may be needed to clear a buffer or something like this.

Hope it helps.