So it sounds like you have DAZ Studio newly sitting alongside Poser 12, and they're on your Dual-Xeon HP workstation (congratulations, good pick) on which you've installed the Apple Mac OS High Sierra?
Now you want all your old DAZ store buys on the new workstation, in DAZ/Iray versions, to run alongside your existing Poser-centric runtime. If so then I would first try to selectively make a big list of the links to the manual download zip files for the DAZ-versions of the store purchases. That's the "Manual install" zip files.
To do this I would first have a "Save selected links as..." browser addon save a local HTML file, for each page in my Product Library links-list.
Then from these locally-saved pages I would have a Sobolsoft tool (or similar utility) extract three lines above and below the following unique HTML tag....
Code:
title=3D"Manual Download">
For some reason the HTML of the saved page has "3D" futzing up the code, as you can see above, and also hard breaks with a "=" breaking link paths. But that's easily fixed. With a little finessing of each text block with a multi-line search-replace tool, you would have a clean list of all the target links - one per line.
The links download their manual zips fine - even if you are not on the page itself, but have moved away to some other order page.
With such a cleaned URL list in hand, I would then have a number of options.
1. Have a downloader addon in your browser download the list's zip files slowly over a few months, ten items a day. Unzip and install manually to wherever your latest version of Daz Studio has its own runtime.
2. Try to get all of the list downloaded continually, via some sort of scripted process. Due to the store logins that would likely have to be browser-based and via a downloader addon. Ideally one that doesn't just try to go get everything at once, but three or four at a time, and has a ten minute pause between each batch. Even then you might trigger some blocking bot, even when logged in.
3. Pay a small-but-willing relative a substantial chunk of pocket-money to spend several days downloading the list manually.