Why aren't my subs turning on?

I have a pair of Von Schweikert VS-3/S subs. Auto-on appears to be the only option, but they do not turn on unless I manually turn them off and then on? They are being fed from the line level (called LFE) outputs of an SMS-1. One to each sub. Both were purchased used from diff owners; hard to believe that they both are independently defective in the same way. They both play when I run the auto-eq frequency sweep. I am sending same question to VS, but your thoughts would help. TIA.