So which forum is currently the one to use because if the xoops site is running on 2.5.6 and none of the forum modules in the downloads come even close the supporting this version. Im a bit stumped. Any suggestions?

you are totally right. no forum module is released officially for xoops 256.

you have 2 unofficial choice:

1- newbb 4.3 Alfred stable version
http://www.simple-xoops.de/projekt/2:1-Forum_-_newBB.html
(there is a newbb 4.4 alpha version too for test)

2- newbb 4.33 irmtfan RC7 version:
http://svn.code.sf.net/p/xoops/svn/XoopsModules/newbb/branches/irmtfan/newbb/

you should choose yourself.

Edit:
personally, I will be glad if you could test my version of newbb and report back any issue or request.
It is mainly a debugged version of all older newbb versions include newbb 1, newbb 2, newbb 3.08, newbb 4, and newbb 4.3