[snip]
I would start the engine the regular way , then use virsh dumpxml HostedEngine > HE.xml
-> edit to your needs.
As you can see if you read carefully the mail, the engine doesn't start at all, due to the unknown feature set: this is the reason I'm going to try to modify it, otherwise I would have no need to interact.
As the engine is not able to start, obviously I cannot dump any xml.....