Thanks again, Amanda, I truly appreciate your help!
I have been playing around a bit and have some additional issues... challenges.
When I use the form on a Marketo landing page, I get available information prefilled. However, using the same form on an Unbounce page, or a plain php page on a separate server (and using the asynchronous munchkin code), the form doesn't prefill.
The progressive profiling works, though none of the already existing information is shown in the form.
Feel free to try yourself; http://eyemobile.tobii.com/spark/EDIT: I found the answer on the forum:
Form Prefill does not work when embedding a form on your own pages. It only works on Marketo landing pages