I'm not really the best person to answer this, as I don't use that hardware or software.
However, if you become a premium member of geocaching.com, you can get pocket queries, which are essentially gpx files with cache data in. You can put those into GSAK, and then export data for the caches you're interested in as a Tomtom POI file. I assume that would allow you to use what you have for caching.
Hopefully someone will be along to give you a fuller answer. If not, you could try posting the question in the Groundspeak UK forum.
Do not go gentle into that good night.
Rage, rage against the dying of the light. (Dylan Thomas)