GH,
try using RB instead.
In RB the ACW allows tempos with decimals that get ridiculously small. WAY more than 3 decimal points.

To 'set the tempo' let the file play through in the ACW while tapping the F8 key on each '1' of the measure. RB intelligently moves the marker to the nearest peak this way, so tapping F8 becomes easier.
Worth a shot. I find this level of detail work much easier in RB than in Biab, and RB should open .sgu files .. much better likelihood for success in RB.

I do not work here, but the benefits are still awesome
Make your sound your own!