hardware of 7755 is better because it has 2 ci slots and 2 card slots, plus it has a faster blind search.
software of 7755 is worse than the 1500, not much worse but the easiest to use and most user friendly is the 1500 model.
Probably more important, the fastest for support and new updates for latest hacks etc is the 1500, and the most popular with users is the 1500. Support and feedback from other owners/users is much better for the 1500 model.
The reason you have got the 7755 is that technomate have a shortage of 1500 models because they cant keep up with demand and so they sell the 7755 model for the same price to trade as a replacement. The new '1500 Super' should become available from next week and hopefully they will be able to keep up with demand, and this will by far be much better than the 7755 and the same price.
Thats the facts so you can make your own mind up as to which is best for you. A technomate is not a sky digibox though, so hope you're not looking to get a sky subscription.