Does ASICBOOST only work on Bitmain miners and how does one enable it on these systems?
"Our ASIC chips, like those of some other manufacturers, have a circuit design that supports ASICBOOST." - Bitmain statement

Bitmain claims that it wasn't used on mainnet. It is currently unknown how to make use of the feature. Likely, you'd need custom firmware and software.



Edit: Here's someone on reddit describing how to activate ASICBOOST: https://www.reddit.com/r/Bitcoin/comments/63yo27/some_circumstantial_evidence_supporting_the_claim/dfy5o65/