Prior to even using it, I upgraded my 990 today, no problem at all, using usb from my laptop.
Can't wait to use it, but must sort the 230V conversion on my 1770 first, basically there's two ways sorting the two toroids getting different voltages (since they're different in size), seems to be either adding a ballast transformer to make a virtual center tap (0-115-230V) or looping a wire through BOTH toroids to force equal voltages, the latter method necessitates removing all 7 amps incl. sockets (arrgghh!!) so I'm going for the ballast toroid, which I ordered locally today (suppose 160VA will be enough, since adding a 0.5A one from my stock already yielded a big improvement over the initial 75V >< 140 V values, i.e. 109 <> 120 V.
The longish board is already working fine (little transformer rewired for 230V) and the big toroids rewired for series primaries.

Well, all gear is finally inn. Once I get things up and running I will post first impressions. Did I ever mention how HEAVY the 7700 is?