As Buzz has said, the Pronto is pretty bit slow when it comes to browsing media catalogues, you would do better to harness the power of your £1200 PC.

By creating a website on the PC that can manage the tasks of interrogating the catalogue, which it then saves to a series of simple CSV or XML files and small JPG for artwork on the website that the Pronto can read/process via HTTP get.

Build actions into the website that can be called via the URL, eg
(note written as h??p so that you can read line rather than it being a link click)

h??p://MyHTPC/MediaManager.php?Catalogue=Films&Genre=Comedy
h??p://MyHTPC/MediaManager.php?SelectItem=12
h??p://MyHTPC/MediaManager.php?Action=Play

It all depends on what media manager you have on the PC and if it has decent (documented) API calls.

I have been playing around with a similar idea using iTunes API ([Link: joshkunz.com])