MSV thank you for your feedback.
We have determined that we can only go with glue down even though we didnt really want to.
As an update for anyone with a similar problem here is what we have done so far:
Ripped up vinyl in the kitchen (put down in 1989 so no concerns of asbestos) and scraped all of the adhesive off the gypcrete. What a PAIN this was (and I mean that literally). We bought a couple of 4" wall scrapers and painstakingly removed old old thick adhesive off about 100 square feet of floor. The gypsum concrete in this area is not in great condition as some of the upper part of it came off with the adhesive.
Removed carpet from another 300 sq ft area and removed carpet adhesive (again with the scrapers). Went through a lot of blades with these two areas but i am really confident that we have got every bit of adhesive off the floor.
Next steps (next weekend) is to prime/seal the gypcrete with Mapei Primer L (probably 2 coats) then apply Mapei Planitex SL (gypsum based self levelling compound) to even out the surface of the floor. There is one area where there is a 1/4" dip that we have to even out and there are some areas that have been damaged by screws so we plan to repair all those and apply a skim coat over the whole 400 square feet. Planitex SL can be applied from featheredge to 1/4".
We then have to wait for the SL to cure and dry (its touch dry in 3 hours and hard in 24 but we need to make sure the moisture levels are appropriate before the next step).
The following weekend we plan to seal the Planitex SL with the Primer L and then put down the cork underlayment. From everything I have researched I believe its best to use urethane adhesive for BOTH the cork and the bamboo even though this adds quite a bit of expensive. I have read that while you can use a latex based adhesive to glue down the cork (cheaper) it is possible that the bond wont be strong enough once the urethane adhesive is used to glue the bamboo to the cork and may pull the cork from the floor. So we will use urethane adhesive (probably Bostik's Best) to glue down the cork and the bamboo.
I think we will probably wait until the following weekend after gluing the cork before starting on the bamboo.
So we still have about four weekends of work ahead of us but I am confident that we have chose the best process for the job (apart from removing the gypsum concrete underlayment which would probably have been best but not an option available to us).
Any thoughts or comments about our proposed process? Any major flaws in it (apart from the unreliability of gypcrete underlayments of course