I do this all the time... but Dreamweaver won't let you do it directly.
You have to:
1) Create your second recordset in Advanced mode with a where clause like: "WHERE DownloadManufacturer = ParamVal" and add a parameter named ParamVal and set its value to: $Downloads->getColumnVal("ManPermalink")
2) Add a repeat region below the existing one (Dreamweaver won't allow you to add it inside)
3) Manually move the second recordset into the the first repeated region
4) Manually move the second repeated region into the the first repeated region below the recordset