Yeah the range looks like: Akka version <= 2.2.4 not Akka version < 2.3.3.  sbt-echo 0.1.1 only gives inspect support up to akka 2.2.4

In the v0.1.1.x of sbt-echo branch I could relax things a bit.  It could support up to Akka 2.3.3 (while still only supporting up to Play 2.2.3 *only*)