I'm in the same boat - utilizing the customer groups (retail, wholesale, and a variety of other groups with discounts). Maybe an oversight? It sure reads like it should allow multiple customer groups for access. I was thinking maybe there was something that could be done with Require Registration for...but that lumps all the registered customers together and I don't think it separates by individual groups.
So along the lines of Mueller's thoughts...I think it's do-able. You can set up multiple hidden content pages that go directly to PDF files OR set up a content page and designate it for a particular group, along with a redirect content page (that says something like "We're sorry, you do not have access to this page)- now anyone registered could see this if it's on a main content page - but they won't get anywhere.
If your downloads and marketing materials are not the same for your various groups, you'd need multiple links on the main content page for all your levels of wholesale/distributors, etc. (you could give each group a name like "Bronze, Silver, Gold, Platinum", by Sales Volume, or something else that they could remember) - and then all they would need to do is click on their individual group name on that page to view their specific information (each link has their individual customer group access, and all have redirects to that same error page).
My last thought is not ideal for marketing materials - but you may be able to utilize it for some things - is to set up some sort of E-products - using the advanced tab you can select multiple groups that have access to these products. Free shipping, non taxable, and Price is zero

. I think you need to upload PDF files to the FTP...but after that I'm not clear on what to do if it's an E-product.
Let us know how you resolve
