Oh well, I've got an RME for the mobo and cpu now.  Scan are going to test them on return and send out a replacement.  They've agreed to first test any replacement parts so hopefully next time everything should be OK.
 

Well, this all went a bit South last night, I superseded my already very high expectations of being able to completely f*** up.
 
So I get home late and tired (delayed train in the morning, broken down [later] train in the evening) and get to work packaging up the motherboard and CPU for returning it today.  The mobo has a plastic cap which protects the socket pins (bed-o-nails).  Try as I might, I just couldn't figure out how the damn thing fitted; it seemed to me at the time 'obvious' that it would clip to the underside of the load plate which would then hold it in place.  However, the outcome of trying to fit it like that completely trashed the CPU socket pins.  The irony is not lost on me.  I subsequently found a picture on the internet which showed that the cap clipped on top of the load plate.  It does wrangle somewhat that I'm going to have to pay for it now after it rocked up DOA but I had little choice other than to 'fess up about being a massive klutz.
 
My first experience with a Supermicro mobo hasn't exactly been the best, but I think I've now found a Gigabyte one for considerably less which has the 2x PCI slots I need.  Watch this space for exciting future developments...

Well, the bitter conclusion of this particular tale of woe|stupidity has now been reached.
 
So I put what I considered to be a generous offer on the table to Scan; I'd accept the hit on the motherboard and buy the Gigabyte one I mentioned, plus some memory from them too.  They completely ignored this.  So that offer got withdrawn, and as the motherboard and CPU were already being returned to them I requested that the CPU be refunded and as before I'd take the hit on the motherboard.  They replied saying that the CPU could not be re-stocked, i.e. due to the cost of a £5 fan which I'd have happily paid for.  Given that, I then decided to take them up on their offer to get the board repaired for a fixed fee of £50.  Over a week goes by, I emailed them several more times chasing them up on what was happening and they finally respond by saying that there would be an additional 'service charge' (on top of the 'fixed price' of £50) of £25 + VAT because they were 'acting above and beyond their normal operating procedures' (their exact words) and that there would be no guarantee whatsoever regarding the efficacy of the repair nor the time frame in which the repair would take place in.
 
This from "a company with a high priority in Customer Service".  So they jerk me around for over a week ignoring my attempts to find out what was happening, then come back to me with an additional charge ne'er before mentioned because they're going so far out of their way with no promise whatsoever that throwing good money after bad would have any beneficial effect.
 
Well.  I kinda lost it at this point.  F*** you Scan! :-D 
 
I might have a Skylake i7 going relatively cheap fairly soon if anybody's interested.