You have to think about the Zu speaker line as an elevator lifting you to escalating resolution and pick your stop -- which floor do you want to get off at? Any Dirty Weekend is Zu's lowest-resolution loudspeaker and least neutral. DWs have the Zu snappiness, dynamic shove and good tone, but they are intentionally ameliorative of upstream system compromises and source material. DWs were intended for entry-level systems and second or vacation home systems where someone might grab a 1970s Marantz receiver off eBay to power them, or some budget electronics today to put together a ~$2500 system with sources. DWs were not meant for obsessive hifi nuts.
Step up to Union 6 and Union 6 Supreme and you have to start seriously considering system synergy. Unions aren't bright or harsh if mated well with associated equipment, but their transparency and musicality depends on solid input from upstream gear. Move up to Soul 6 and you have a true high-end speaker in a relatively affordable, compact form that will absolutely not smooth over flaws in upstream gear. But feed them properly and they will reward you with clean, expressive, explosive, tone-dense, beautiful sound that you can listen to all day long. Steve Guttenberg simply didn't take the time to understand the Soul 6 and completely flubbed his review. Look for Sam Rosen's Positive Feedback review, and and John Darko's commentary for a more educated and realistic assessment. Guess what -- all this applies to Druid 6 even more so and Definition 6 will mesmerize you (I have the first pair) if you have upstream gear commensurate to them.
The new Griewe-out-the-back scheme in Unions and Definition 6 certainly simplifies setup and bass optimization compared to the bottom-exited Griewe models. You just have to figure out how much musical objectivity you want to optimize your system for. You can be lazy about that with Dirty Weekends. You can be casual about that with Union 6. You have to start thinking systemically with Union 6 Supreme. Soul 6 and above, lazy and casual system thinking won't cut it.
Phil