Just a quick update: no building this weekend as I have been struck with cold/flue. I have no energy to do anything so I'm resting as much as possible. A bit frustrating really much nothing I can do about it. One thing I did do was order a 7m HDMI cable from eBay to complete the cabling between the DAW and the room. Hopefully I'll be feeling better by next weekend.
The only other I have done is to estimate the mineral wool requirements for the corner chunks. It works out that I'll need 29 slabs which leaves 4. Not too bad because I used a lot more to fill the ceiling than originally planned. I knew there would be excess because I hadn't taken the stud framework into account when estimating the volume required. This means I'll probably only need another 2/3 bales (4 slabs) for additional room treatments. I can worry about this later. Anyway, enough for now...