Thanks for your advice.
1. I've gone back to the previous set of files created by the DA Wizard and created a recordset, which I've called rs_getOptions. This then populates a list of options with checkboxes on the Insert page (via repeat region on a <ul>).
2. I've added a Manage Relational Table behaviour to the page
(it shows as Manage Relational Table (productoptions) in the Server Behaviors list), and despite trying both 'Button Insert pressed' and 'any form post' as triggers, only the Products table is being updated; nothing appears in the productoptions table.
As I'm probably doing something wrong in the Manage Relational Table wizard I've attached screenshots of my entries so you can see what I've done.