I'm afraid that I haven't made much more progress. I've emailed One For All and Universal Electronics and have not had a reply yet. I've also checked on their web sites to see if they list our Set Top Box and they do not list any Pace cable boxes.
If you want more info on the One For All and using it to simulate IRDA codes, especially if you're thinking of buying one, then your best bet is to talk to Andy Rivers at Video Precision (01367 850111). He told me that you can download codes into a One For All over the telephone. You can then use it to teach a Pronto. It appears that the One For All transmits conventional IR codes but can still control IRDA devices.
Sadly, I'm not sure that the database of 80,000 codes includes our set top box. I've emailed them asking this question and am awaiting a reply.
Our set top box is still quite new, so maybe it's just a question of time before they add it to their database. I've asked them about it, so maybe if a few more people ask them, they'll do something about it.
I'm getting more and more fed up with using two remotes. We've got to get this sorted.