Wow...
You were at MPW, right?
I'm sure that there are people who are more current on this than I,
but since I got you into it in the first place, I guess I'm
responsible :-)
Hypam is Ilford's version of rapid fix, as I recall (it isn't too
popular in the US). Just guessing, but I'd be a little concerned about
using an ammonia thiosulfate fix instead of sodium, but if that's all
you have, then a little experimenting might be in order.
At its normal working strength, you will probably find that Hypam is too
strong & will destroy the image. You could dilute it, first by half,
then 1:2, and so on, to see its effect on the image. Once you find a
dilution that doesn't harm the image, then your next concern is whether
or not the image is fixed enough. Try cutting a test print in half and
putting one piece in a dark place and exposing the other to strong day
light (avoiding direct sunlight). If there is any undissolved, non-image
silver, I would expect it to print out after a few hours and become visible
as a brown fog.
This is probably not the best answer, but it should give you a direction
to pursue.
Happy printing,
Carson Graves
carson@ileaf.com