Scalaでtypeをダイアモンド継承する際に綺麗に書けない

Diamond.scala

trait A {
  type X <: AA
  trait AA
}

trait B extends A {
  type X <: AA with BB
  trait BB
}

trait C extends A {
  type X <: AA with CC
  trait CC
}

trait D extends B with C {
  type X <: AA with BB with CC // ここなんとかしたい
}

class E extends D {
  type X = EE
  val x = new X
  class EE extends AA with BB with CC // ここも
}

Diamond2.scala

trait A {
  type X <: A.XX
}

object A {
  trait XX extends AA
  trait AA
}

trait B extends A {
  type X <: B.XX
}

object B {
  trait XX extends A.XX with BB
  trait BB
}

trait C extends A {
  type X <: B.XX
}

object C {
  trait XX extends A.XX with CC
  trait CC
}

trait D extends B with C {
  type X <: D.XX
}

object D {
  trait XX extends B.XX with C.XX
}

class E extends D {
  type X = EE
  val x = new X
  class EE extends D.XX
}