I believe ‘back order’ is the status it gets when it won’t be shipped right away, as in the case of a preorder. My order was from the 12th and still shows backorder. However, if you order now, it says it will ship on June 19th.

According to the Amazon web site.  The Sub G3 is not available for order until June 16.  The Arc is showing June 10.  So, maybe the 5.1.2 system can’t be shipped in it’s entirety until the Sub’s are ready for shipment.  I realize you ordered from Sonos directly.  But I find the Amazon date to be interesting, in light of your information.

Amazon has been known to be wrong before. I never take their information as gospel.

I don’t shipping dates for orders made to day can really tell you much about orders that were already placed.  As well, different retailers are going to have different levels of stock, and when they expect replenishment.

Amazon is offering the Arc, Sub, and two SL’s as a package at a $358 discount to list price on US site.

Update:  Now it’s been removed.  - Odd.