In 2007 when I purchased an Xbox 360, I started a new Xbox account - no issues there
In November 2013 I started a new custom domain account on Outlook, which I use to sign into Windows 8.1 - no issues there

However, I wanted to see what apps and games were available in Windows 8.1 it tells me I need an Xbox Live account - and I do, but not on the Windows 8.1 account.

My Google (or Bing) skills to find instructions from Microsoft to see if it is possible to merge must be poor as I can not find
I do not wish to loose my achievements in the process

Can anyone point me in the right direction?
Thanks