I've read that .... and the question I asked is not answered there. Hence asking it both on Twitter when I asked @Zac Cocken and here and as yet still have no answer to the question.
I can put the question another way if you prefer?
I already have a PC account can the xbox account stuff be transferred to the already existing PC account or do I need to create a NEW Account/CMDR on the PC for everything to be transferred to?
The account can merge in-terms of purchased cosmetics etc but you won't be able to merge your save data. If you want to transfer your Commander data on console to an already existing account on PC, you'll have to delete the Commander save data that already exists on that account on PC.
If you'd rather keep both, you can create a new Frontier account using a different email address during the transfer process that will give you a free copy of Horizons on PC, that your console Commander data will be transferred to.