Commerce Product Display Manager is not necessary, I've gotten this to work and I've never used that module.
I went for the route of automatically creating a Node after saving the Product.
Below is my Rules export for this:
{ "rules_create_product_display" : {
    "LABEL" : "Create Product Display",
    "PLUGIN" : "reaction rule",
    "REQUIRES" : [ "rules", "entity" ],
    "ON" : [ "commerce_product_insert" ],
    "IF" : [
      { "data_is" : { "data" : [ "commerce-product:type" ], "value" : "**PRODUCT_TYPE**" } }
    ],
    "DO" : [
      { "entity_create" : {
          "USING" : {
            "type" : "node",
            "param_type" : "**NODE_TYPE**",
            "param_title" : "[commerce-product:title]",
            "param_author" : [ "commerce-product:creator" ]
          },
          "PROVIDE" : { "entity_created" : { "entity_created" : "Created entity" } }
        }
      },
      { "data_set" : {
          "data" : [ "entity-created:**PRODUCT_REFERENCE**" ],
          "value" : [ "commerce-product" ]
        }
      }
    ]
  }
}
You'll need to substitute your own values for:
- PRODUCT_TYPE (product type that has been created)
- NODE_TYPE (node type being created)
- PRODUCT_REFERENCE (field that will reference the created product)
Sorry I can't dedicate more time to a better answer now, let me know if you'd like me to elaborate on the process of creating the above using the GUI