6 units, for two days' production, seems incredibly low. The Ultras came much quicker than that when parts were available. I'm wondering if something has a high failure rate on burn in. [/total speculation]
As with any technical endeavor, "it's all in the technique." Once they get their groove on, they'll double-time it. And remember, Cliff promised that QC was #1, so they'll be very rightfully cautions and slow at first. If I was doing it, I would keep my assembly crew small at first to keep a close eye on everything. Then, once you know what you're doing, expand to more staff and quicker techniques. And then you can cut out areas of QC where there is never ever an issue.