Right, there are a couple of options that Williow Technologies have discussed, but the one that is most likely would be something called a SENtral M&M Module. However, whatever genius came up with these products decided it was a good idea to get the hardware to output in something called a Quaternion Matrix.
It is a table of vector based values which can be converted to relative position and rotational value. However he mentioned that it is some extremely complicated maths... great.
Saying that, the kit is only around £100 so it may be worth sticking with.
I'm going to research it, but if anyone knows anything about converting a Quaternion Matrix, give me a shout!
Edit: Found this site which my help the process of back calculating the figures: