Jims Correct,
I worked mine out in the following way which may help.
10 tooth sprocket on the TAV
60 tooth sprocket on the layshaft
41 tooth sprocket on the other end of the layshaft
45 tooth sprocket on the diff.
10x41= 410
60x45 = 2700
2700/410.53 = 6.585
I have a similar set up but a 40 tooth sprocket on the layshaft.