For those of you who still cannot find a proper way to use a 32-bit DLL under a native 64-bit IIS Application Pool, either by tweaking the registry, or by trying how to deal with the "COM+ Components Services", and if you absolutely need to run the IIS Application Pool in 64-bit" (so turning "Enable 32-bit Applications OFF") : I have found a perfectly working solution : "Encapsulating" the 32-bit component into a new COM object as described on this page did the job perfectly, and I think that a lot of you will be interested to solve the problem this way ;)
In my case, that allowed me to use the "XStandard.Zip" free Component from XStandard, which is sadly only available as a 32-bit ASP component, and that have an "InProcServer32" Key in the registry apparently preventing it to work by tweaking the registry, as described here : https://techtalk.gfi.com/32bit-object-64bit-environment/
In this post, a lot of comments reported that "InProcServer32-IDs are not reflected because Microsoft assumes that these are only InProc-Calls and not Out-Of-Proc-Calls".
And that was my case too, leading me to the situation where the registry tweaking solution described in the previous post was not working in my case, as other users.
Hoping having saved some days... or nights !