Spent considerable time ...

Spent considerable time working on Se reduction and it is not as easy as folks try to make it. Se can exist in an oxidized or reduced form as well as elemental.

Anyone that claims to have a solution and the 1st step in their solution is not to get your sample speciated doesn't have a working knowledge of Se.

So in keeping with my own advice, you must get your sample speciated so you know what you have. 

Here is a simple example. ferric precipitation works really well with selenite. Not so hot with selenate. So you can reduce selenate to selenite with ferrous and get a double benefit with the ferric formed when ferrous is oxidized the ferric. Now have a little selenothionate. It cannot be reduced since it is a reduced form. You can decrease the Se+3 and Se+4 to low ppb but 10ppm from Selenothionate stays 10ppm.

Hope that helps.